Engine Terminology

1. Engine Terminology Engine Measurement Lesson 8 March 2008

2. Engine Size Measurement • Engine size is determined by the cylinder diameter, the amount of piston travel (stroke) and the number of cylinders.

3. Bore and Stroke

4. 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)

5. 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)

6. Changing Bore Size What happens if the engine is bored? Definition: Boring • Material is moved from the cylinder walls and a larger piston is installed Displacement & compression ratio are both increased when bored (AKA “bored out”) How would the displacement of a stock 6 cylinder engine with a bore of 4.000” and a stroke of 3.000” change if it were bored 0.060”?

7. Changing Length of Stroke What happens if the engine is stroked? Definition: Stroked • Changing the crankshaft offset (installing a new crankshaft) Displacement & compression ratio are both increased when stroked How would the displacement of a stock 6 cylinder engine with a bore of 4.000” and a stroke of 3.000” change if it were stroked 0.125”?

8. Change of Bore and Stroke What happens if the engine is bored & stroked? • Changing the crankshaft offset and boring the cylinder How would the displacement of a stock 6 cylinder engine with a bore of 4.000” and a stroke of 3.000” change if it were stroked 0.125” and the bore 0.060”?

9. Oversquare and Undersquare

10. How to increase engine output • How to increase engine output Increase volumetric efficiency • Better gas flow • Forced induction • Altered valve timing • Improve engine efficiency • Better combustion efficiency • Lower internal friction • Reduce heat loss • Better fuel

11. 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  strokedisplacement 4 OR piston = bore  bore 0.7854  strokedisplacement

12. Example of Piston DisplacementFormula If an engine has a bore of 4" and a stroke of 3", what is it’s piston displacement? piston displacement = (42)  3.14  3 4 16  3.14  3 4 150.72 4 = 37.68 (cu. in.) 4 x 4 x .7854 x 3 = 37.69 (cu.in.) OR

13. Volumetric Efficiency • Ratio of air drawn into the cylinder and the maximum amount of air that could enter the cylinder • Simply put, it is the ability of the engine to breath in on the Intake Stroke Formula: Volumetric Efficiency = actual volume of air taken into each cylinder volume of the cylinder

14. Factors that impact Volumetric Efficiency Engines are capable of only 80–90% volumetric efficiency. Restrictions in the ports and around the valves limit airflow. Can you name some of the factors that would impede air flow into and engine?

15. Is ‘volumetric efficiency’ the same as cylinder volume? 8 to fill 1 to fill BDC TDC

16. Swept and Clearance Volume

17. Compression Ratio Compares the cylinder volume with the piston at TDC to the cylinder volume with the piston at BDC • Ratio of swept volume V1 divided by combustion chamber volume V2

18. Compression Ratio – Gas Engine

19. Compression Ratio – Diesel Engine

20. High Compression RatioPros and Cons • Higher compression gives greater combustion efficiency, up to a point • Efficiency goes down after a certain point due to need to retard ignition timing to avoid knock

21. Volumetric Efficiency and Compression Ratio Relationship • Volumetric efficiency is: • Ratio of air drawn into the cylinder (by the intake stroke) and the maximum amount of air that could enter the cylinder (restricted by design of intake passages, size of valve openings, valve timing and overlap ). • Compression ratio is: • Ratio between the cylinder volume when the piston is at TDC compared to when it is at BDC.

22. Compression Pressure Checking the Seals How is it measured? What unit of measurement is used? (Answers on next slide) • 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)

23. Measuring Combustion Pressure • 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 (engine seal)

24. Brake Mean Effective Pressure • Not actually a measure of pressure, just expressed in pressure units (N/m2 or psi) • A measure of work output from an engine • BMEP = Horsepower__________ (Swept volume Vs) ( rpm/120)

25. Examples of 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

26. Conversion of Measurement 61.02 cubic inches = 1 litre From litres  cubic inches 5.0L x 61.02 = 305CID From cubic inches  litres 305 / 61.02 = 5.0L 1L = 1000cc 1 cu. in. =16.39cc

27. 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) bore  bore 0.7854  stroke x cylinder number