Internal Combustion Engine Terminology

Engine Efficiency

• Volumetric efficiency is the percentage of the cylinder's volume that is filled with air at normal temperature and pressure, calculated by dividing the weight of the gas entering the cylinder by the weight of the gas that would fill the cylinder at normal temperature and pressure, multiplied by 100.
• Most engines are approximately 80% efficient.

Valve Operation

• Valve lead refers to the opening of a valve before its theoretical stroke, for example, the exhaust valve opening before bottom dead centre (BDC).
• Valve lag refers to the closing of a valve after its theoretical stroke, for example, the inlet valve remaining open after BDC.
• Valve overlap occurs when both the intake and exhaust valves are open at the same time.

Firing Order

• The firing order for an inline 4-cylinder engine is 1, 3, 4, 2.
• The firing order for a horizontally opposed engine is 1, 4, 3, 2.
• The firing order for a 6-cylinder engine is 1, 5, 3, 6, 2, 4.

Engine Design

• Engines with high compression ratios require the spark to be advanced.
• Twice the crank throw is equal to 1 stroke.
• The camshaft rotates at half the crankshaft speed.

Valve Train

• The tappets are measured between the rocker pad and the valve top or valve stem.
• Valve springs are used to close the valves.
• Multiple springs are used to prevent valve bounce.

Piston Design

• Compression rings are located on the side of the crown of the piston.

Oil System

• The scavage pump has a greater capacity than the supply pump.
• The oil pressure gauge is situated between the supply pump and the engine.
• Coring occurs when the oil cooler matrix is blocked with high-viscosity oil.
• The anti-surge valve opens to bypass the oil coolers and prevent coring when high-viscosity oil is pushed to the oil cooler at startup.
• The check valve prevents most of the oil from running back to the sump.