Engine Terminology

Measuring Engine Performance

Lesson 7

March 2008

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.

Engine Torque Specs

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)

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.

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

Horsepower FormulaRemember laws of mechanics (physics)

work = Distance (ft.) Moved x Force (lbs.) Applied

Horse power example

BHP & IHP

IHP – Indicated Horsepowerpower formed in the combustion chamber

BHP – Brake Horsepowerusable power at the engine crankshaft

There is a third HP rating that is important

**WARNING**

Horse Power Loss

Friction and Load (HP robbers)

Can you describe the difference between friction and load?

Engine Friction

What are the components that cause engine friction?

Engine Load

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

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)

Efficiency

How efficient is the four stroke cycle engine?

20 % or less to do work

5% loss to engine friction and load2 % chassis and transaxle weight3 % tire resistance2 % loss to aerodynamics 35 % Cooling system35 % Exhaust system

.80 cents of every dollar thrown away

Designed Loss of Efficiency

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

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

Thermal Efficiency

Thermal efficiency is the measured comparison betweenhorsepower 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 20-30 %.

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

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 sizeFormula thp = bore squared x number of cylinders x .04

Reducing Friction

Low tension piston rings

Thinner piston rings

Low tension valve springsLighter valves allow lower tension valve springs

Low-friction coatingsMain and rod bearingsPiston skirtsCam lobes and followers

Mechanical Efficiency

Mechanical efficiency compares the difference between Brake Horsepower (BHP) and Indicated Horsepower (IHP).

If 70-80% mechanical efficiency is normal, then the lost horsepower was caused by our horsepower thieves and Frictional Horsepower.

FHP(frictional) = IHP(indicated) – BHP(brake)

Example : 30 (IHP) – 25(BHP) = 5 FHP

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).

Engine Dynometer

• measuring engine performance without driveline frictional losses

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

Dyno Performance Chart

2.0 liter

150 @ 6,400 rpm

141 @ 5,200 rpm135 @ 5,200 rpm

Engine

HP (Dodge.com)

Lb-Ft

Example of Engine Rating