Slide 1

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 2

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 3

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 4

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 5

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 6

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 7

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 8

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 9

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 10

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 11

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 12

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 13

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 14

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 15

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 16

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 17

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 18

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 19

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 20

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 21

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 22

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 23

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 24

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 25

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 26

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 27

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 28

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 29

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 30

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 31

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 32

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 33

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 34

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 35

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 36

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 37

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 38

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 39

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 40

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 41

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 42

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 43

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 44

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 45

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 46

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 47

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 48

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only


Slide 49

by
Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only








Engine size measurement
Force, work, and power
Compression ratio
Engine torque
Horsepower
Engine efficiency

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Engine size is determined by the
number of cylinders, the cylinder
diameter, and the amount of piston
travel per stroke
 Engine size information is used when
ordering parts and when measuring
wear during major repairs
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Cylinder Bore
 Diameter of the engine cylinder
 Measured across the cylinder, parallel
with the top of the block
 Cylinder bores vary in size, but typically
range from 3–4" (75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Stroke
 Distance the piston moves from top
dead center (TDC) to bottom dead
center (BDC)
 Crankshaft journal offset (throw)
controls the piston stroke
 Stroke varies from about 3–4"
(75–100 mm)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Bore and Stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Piston Displacement
 Volume the piston displaces as it
travels from BDC to TDC
 Found by comparing cylinder diameter
and piston stroke
 Piston displacement formula:
piston
displacement

© Goodheart-Willcox Co., Inc.

=

bore squared  3.14  stroke
4

Permission granted to reproduce for educational use only

Piston Displacement
If an engine has a bore of 4" and a stroke
of 3", what is its piston displacement?
piston
displacement

=
=
=
=

© Goodheart-Willcox Co., Inc.

(42)  3.14  3
4
16  3.14  3
4
150.72
4
37.68 cu. in.
Permission granted to reproduce for educational use only

Engine Displacement
 Volume displaced by all the pistons in
an engine
 piston displacement multiplied by the
number of cylinders

 Units of engine displacement:
 cubic inch displacement (CID)
 liters (L)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Displacement
If one piston displaces 25 cu. in. and the
engine has four cylinders, what is the
engine displacement?
25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the
engine has six cylinders, what is the
engine displacement?
500 cc  6 = 3000 cc
= 3.0 L
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Force
 Pushing or pulling action
 Measured in pounds or newtons
 When a spring is compressed, an
outward movement and force is
produced

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Work
 Occurs when force causes movement
 Measured in foot-pounds or joules
 Formula for work:
work = distance moved  force applied

For example, if you use a hoist to lift a
400 pound engine 3 feet in the air, how
much work has been done?
work = 3'  400 lb
= 1200 foot pounds (ft lb)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
 Rate, or speed, at which work is done
 Measured in foot-pounds per second or
per minute
 The metric unit for power is the watt or
kilowatt
 Formula for power:
power = distance  force
time

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Power
If an engine moves a 3000 pound car
1000 feet in one minute, how much power
is needed?
power = 1000'  3000 lb
1 minute
= 3,000,000 ft lb
min.

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compares the cylinder volume with the
piston at TDC to the cylinder volume with
the piston at BDC

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
This engine has eight
times the volume at
BDC, producing an 8:1
compression ratio

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
 Formula for compression ratio:
compression
ratio

= cylinder volume at BDC
cylinder volume at TDC

 Use of high compression ratio:
 increases engine fuel efficiency and
power
 increases exhaust emissions (NOx)
 increases risk of detonation

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Gasoline Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Ratio
(Diesel Engine)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Pressure
 Amount of pressure in the cylinder on
the compression stroke
 Measured in pounds per square inch
(psi) or kilopascals (kPa)
 Gasoline engine compression
pressure:
 130–180 psi (900–1200 kPa)

 Diesel engine compression pressure:
 250–400 psi (1700–2800 kPa)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Compression Gauge
 Used to measure compression
pressure
 Using a compression gauge:
 screw the gauge into the spark plug,
injector, or glow plug hole
 crank the engine
 note compression gauge readings

 Gauge readings are a good indicator of
engine mechanical condition
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Rating of the turning force at the engine
crankshaft
 When combustion pressure pushes the
piston down, a strong rotating force is
applied to the crankshaft

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Torque
Specifications
 Given in a shop manual
 Torque specification example:
 450 ft lb @ 3000 rpm
 engine would be capable of producing a
maximum of 450 ft lb of torque at an
operating speed of 3000 revolutions per
minute

 The metric unit for engine torque is
newton-meters (N•m)
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Measure of an engine’s ability to
perform work (power)
 At one time, one horsepower was the
approximate strength of a horse

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower

One horsepower equals 33,000 ft lb of
work per minute
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
 Formula for horsepower:
horsepower = work (ft lb)
33,000
Or
horsepower = distance (ft)  weight (lb)
33,000

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Horsepower
For a small engine to lift 500 pounds a
distance of 700 feet in one minute, about
how much horsepower is needed?
hp = 700'  500 lb
33,000
= 10.6 hp

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Factory Horsepower
Ratings
 Given in a shop manual
 Automobile makers rate engine power
at a specific engine speed
 Horsepower example:
 400 hp @ 5000 rpm

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Brake Horsepower (bhp)
 Measures usable power at the engine
crankshaft
 Horsepower was first measured with a
prony brake
 Braking was applied to the engine
crankshaft, causing a force on a scale
 Horsepower was read from the needle
deflection
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Prony Brake

Measures engine horsepower
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer
 Used to measure the brake horsepower
of modern car engines
 Either an electric motor or a fluid
coupling is used to place a drag on the
engine crankshaft
 allows power to be determined

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Engine Dynamometer

Using a dynamometer to measure
engine performance
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer
 Measures the horsepower delivered to
the rear wheels
 Indicates the amount of horsepower
available to propel the car
 Accounts for any power consumed by
the drive train

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Chassis Dynamometer

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Indicated Horsepower (ihp)
 Refers to the amount of power formed
in the engine combustion chambers
 Pressure-sensing equipment is placed
in the cylinder
 Pressure readings are used to
determine the indicated horsepower

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Frictional Horsepower (fhp)
 Power needed to overcome engine
friction
 Indicates the resistance to movement
between engine parts
 Reduces the amount of power left to
propel the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower
 Also called SAE net horsepower
 Maximum power developed when an
engine is loaded by all accessories
 alternator, water pump, fuel pump, air
injection pump, air conditioning, and
power steering pump

 Indicates the amount of power
available to move the car

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Net Horsepower

Available horsepower with the engine
operating all accessories
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Gross Horsepower
Power available with only basic
accessories installed–alternator, fuel
pump, and water pump

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Taxable Horsepower
 General rating of engine size
 In many U.S. states, it is used to calculate
the tax placed on a car
 Taxable horsepower formula:
thp = bore squared  number of cylinders  0.4

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

 Ratio of usable power at the crankshaft
(brake horsepower) to the power
supplied to the engine (heat content of
fuel)
 By comparing fuel consumption to
engine power output, you can find
engine efficiency
 Most engines are about 20% efficient

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Ratio of air drawn into the cylinder and
the maximum amount of air that could
enter the cylinder
 Indicates how well an engine can
“breathe” on its intake stroke

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Volumetric Efficiency
 Engines are capable of only 80–90%
volumetric efficiency
 Restrictions in the ports and around the
valves limit airflow
 Volumetric efficiency formula:
volumetric = volume of air taken into cylinder
efficiency
volume of cylinder

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Mechanical Efficiency
 Compares brake horsepower and
indicated horsepower
 Measurement of mechanical friction
 Mechanical efficiency of 70–80% is
normal
 20–30% of the engine’s power is lost to
friction (frictional hp loss)

© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only

Thermal Efficiency
 Found by comparing the horsepower
output to the amount of fuel burned
 Indicates how well an engine uses the
fuel’s heat energy
 Engine thermal efficiency is about
20–30%
 70–80% of the heat energy is absorbed
by the metal parts of the engine and
blown out the exhaust
© Goodheart-Willcox Co., Inc.

Permission granted to reproduce for educational use only