Compression Ratio: In an internal combustion engine, the measurement of the difference between cylinder volume at BDC and TDC. This is the ratio of the maximum-to-minimum volume within the cylinder, between the piston and cylinder head, containing a combination of fuel and air being compressed. A high compression ratio results in more mechanical energy that an engine can squeeze from its air-fuel mixture. High ratios place increased oxygen and fuel molecules into a reduced space: thus, they allow increased power at the moment of ignition. Compression ratio is a single number that can be used to predict engine performance.

 

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