1. Measuring Engine Performance page 91
Chapter Brian
Measuring Engine Performance
page 91

2. Basic Terminology Bore & Stroke Engine Displacement Compression Ratio
Force
Work
Power
Energy
Horsepower

3. Bore
Diameter of cylinder
2 X Radius

4. Stroke
Distance
TDC-BDC
Distance piston travels
up or down

5. Cylinder Displacement
x D2 x stroke or
Π x r2 x Stroke

6. Engine Displacement 0.7854 x D2 x stroke X # of cylinders or
Π x r2 x Stroke # of cylinders
in3 / 62 = Liters

7. Compression Ratio Area of cylinder at BDC compared to
Area of cylinder at TDC
63 in3 to 9 in3 =
7:1 compression ratio

8. Force pushing or pulling stationary force moving force
Centrifugal force
spinning
FORCE does NOT = Pressure

9. Pressure Pressure is force per given area or Force/Area PSI
Force = psi X area
Area = force / psi
Area = Π R2

10. Work force applied resulting in movement Work = Force x Distance
W = F x D
Mechanical advantage (lever, ramp, etc)
Effort distance / resistance distance = Mechanical advantage

11. Mechanical Advantage 10’ / 2’ = 5 = MA E(effort) = R(resistance)/ MA
500# 2’

12. Power Power is time taken to do the work P = work/time P=W/T
Power = feet x Pounds / time
or Foot pounds per second?

13. Energy Energy can not be created or destroyed
Potential—has the potential to . . .
Kinetic
Mechanical
Chemical
Thermal (heat)
Light

14. Horsepower Power = work / time P= w/t
Hp = 33,000 ft-lb (work) / 1 minute (time) or
Hp = 550 ft-lb / 1 second

15. Horsepower Formula 100 ft x 330 lb / 6 seconds = 5500 ft lb / sec
dividing this by 550 ft lb / sec (1hp) =
(5500 ft-lb /sec) / (550 ft lb / sec) = 10 hp
thus
1 hp = rate of work in ft-lb/sec / 50 ft-lb / sec

16. Kinds of Horsepower Brake Horsepower Indicated Horsepower
Frictional Horsepower
Rated Horsepower
Corrected Horsepower

17. Brake Horsepower
bhp
actual hp delivered
what we can use

18. Indicated Horsepower ihp (perfect world)
power developed by the burning fuel
average of power on 4 strokes (mean)
PLANK / 33,000
P = mep in in lb/in2
L = length of stroke
A = Cylinder Area
N = power strokes per minute or RPM / 4
K = # of cylinders

19. Frictional Horsepower
fhp
HP lost because of drag
fhp = ihp-bhp

20. Rated Horsepower
rhp
80% of bhp

21. Corrected Horsepower corrected for elevation (sea level)
corrected for temperature
barometric pressure
quality of fuel
humidity

22. Torque
Twisting force
force x distance
ft - lb
in – lb
Newton - Meters

23. Torque is not Constant Torque will change w/ engine speed
More pressure on piston = more torque

24. Torque and Horsepower Unlike torque. . .
Horsepower increases with engine speed
Torque measure of engine’s twisting force
Hp measures engine’s ability to do work

25. Volumetric Efficiency
How well an engine breathes
draws air/fuel into cylinder
Can decrease as engine speed increases
many factors

26. Practical Efficiency
how efficiently an engine uses the fuel

27. Mechanical Efficiency
% of power developed in cylinder (ihp)
compared to
power delivered to crankshaft (bhp)
friction,
Mechanical efficiency = bhp/ihp

28. Thermal Efficiency Heat efficiency
how much power produced is used to push the piston down
Power is lost to :
cooling
exhaust
20-25% efficient
Exhaust 35% . . .
Cooling & Lubrication 35%

29. Brake thermal efficiency=
Brake horsepower (bhp x 33,000)
778 Fuel heat value x weight of burned fuel per minute
778 is Joule’s equivalent
it is a constant