Compression Ratio

Definition - What does Compression Ratio mean?

Compression ratio is defined as quite simply as the volume above the piston at bottom-dead-center (BDC), divided by the volume above the piston at top-dead-center (TDC). High compression motors require the use of high octane gasoline to prevent pre-ignition and or detonation which can cause costly damage to pistons, valves, and piston rings or even worse, losing the race. Compression Ratio is an important variable in building a performance engine.

Petropedia explains Compression Ratio

Generally, cylinder pressure for common automotive designs should at least equal 10 bar , or, roughly estimated in pounds per square inch (psi) as between 15 and 20 times the compression ratio, or in this case between 150 psi and 200 psi, depending on cam timing.

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