The squeezing of the air/fuel mixture by the upward movement of the piston (in the cylinder).

Compression can be changed by using different pistons, changing the overall size of the cylinder, cylinder heads or changing the crankshaft.

The higher the compression ratio the more power the engine can produce.  Lower compression ratios have been in most vehicles today to help with better emissions of the exhaust. There is a fine line between high and low compression and emissions output in the exhaust.

Leave comments below or see these