© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois by Russell Krick

© 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 bore squared  3.14  stroke displacement 4 =

© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only If an engine has a bore of 4" and a stroke of 3", what is its piston displacement? piston (4 2 )  3.14  3 displacement 4 16  3.14  cu. in. = = = = Piston Displacement

© Goodheart-Willcox Co., Inc. 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 This engine has eight times the volume at BDC, producing an 8:1 compression ratio Compression Ratio

© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only  Formula for compression ratio: compression cylinder volume at BDC ratio cylinder volume at TDC  Use of high compression ratio:  increases engine fuel efficiency and power  increases exhaust emissions (NO x )  increases risk of detonation = Compression Ratio

© 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 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 (Nm)

© 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:  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: volumetricvolume 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