1. Measuring Engine Performance
Engine Terminology
Measuring Engine Performance
Lesson 7
March 2008

2. Definition of Engine Torque
Turning or twisting force that causes a body to turn (rotate).
Torque = Length x Force Applied
Engine torque is a rating of the turning force (torque) at the crankshaft end. Engine torque specifications can be found in shop manuals.

3. Engine Torque Specs Given in a shop manual
Torque specification example:
450 ft 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)

4. Definition of Horsepower
Horsepower is the rate at which torque is produced.
One horsepower is equal to 33,000 foot-pounds of work in one minute.
One horsepower is equal to 746 watts, 545 Btu, 1055 joules, or 252 gram-calories.

5. 1 HP is equal to 33,000 ft.lbs. of Work

6. Horsepower Formula Remember laws of mechanics (physics)
work = Distance (ft.) Moved x Force (lbs.) Applied

7. Horse power example

8. BHP & IHP BHP – Brake Horsepower usable power at the engine crankshaft
IHP – Indicated Horsepower
power formed in the combustion chamber
There is a third HP rating that is important

9. **WARNING**
Horse Power Loss

10. Friction and Load (HP robbers)
Can you describe the difference between friction and load?

11. What are the components that cause engine friction?

12. What components cause engine load?
Does it not take horse power to drive these accessories?

13. FHP (Frictional Horse Power) The power needed to overcome engine friction and load
IHP (Indicated Horse Power) _
FHP (Frictional Horse Power) =
BHP (Brake Horse Power)

14. Efficiency How efficient is the four stroke cycle engine?
5% loss to engine friction and load
2 % chassis and transaxle weight
3 % tire resistance
2 % loss to aerodynamics
35 % Cooling system
35 % Exhaust system
20 % or less to do work
.80 cents of every dollar thrown away

15. Designed Loss of Efficiency
Do you remember our discussion about engine friction and load?
Now you can see the impact they have on efficiency.

16. 2 Greatest Wastes of Power?
Exhaust System 35%
Cooling System 35%

17. Thermal Efficiency
Thermal efficiency is the measured comparison between
horsepower output in relation to the amount of fuel burned to create this power.
To look at it differently, thermal efficiency is the measurement of how well the engine uses the energy (heat) produced from combustion (burning fuel charge) to turn the crankshaft.
Normal rating is %.

18. Keep the Heat
In general, less heat rejected to the cooling system or atmosphere results in more heat energy to be converted to mechanical energy
Exhaust coatings and wraps
Coated piston crowns

19. FHP / NHP /GHP /THP
NHP – Net Horsepower – maximum power developed by an engine when all accessories on
GHP – Gross Horsepower – maximum power developed with only minimum accessories on
THP – Taxable Horsepower – rating of engine size
Formula
thp = bore squared x number of cylinders x .04

20. Reducing Friction Low tension piston rings Thinner piston rings
Low tension valve springs
Lighter valves allow lower tension valve springs
Low-friction coatings
Main and rod bearings
Piston skirts
Cam lobes and followers

21. Mechanical Efficiency
Mechanical efficiency compares the difference between Brake Horsepower (BHP) and Indicated Horsepower (IHP).
If % mechanical efficiency is normal, then the lost horsepower was caused by our horsepower thieves and Frictional Horsepower.
FHP(frictional) = IHP(indicated) – BHP(brake)
Example : (IHP) – 25(BHP) = 5 FHP

22. Engine Efficiency
Engine efficiency is the ratio of BHP (Brake Horsepower) to the power produced by the burning of a fuel charge (combustion) in the engine cylinders.
BHP in relation to Fuel quantity = Engine efficiency
As previously seen, only an average of 20% heat energy is available to do work (turning crankshaft).

23. Engine Dynometer
measuring engine performance without driveline frictional losses

24. Chassis Dynometer 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

25. Dyno Performance Chart

26. Example of Engine Rating
2.0 liter
6,400 rpm
5,200 rpm 5,200 rpm
Engine
HP (Dodge.com)
Lb-Ft