compression ratio

American  

noun

Automotive.

1. the ratio of the cylinder volume enclosed by the piston at its outermost position to the volume enclosed by it at its innermost position.

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compression ratio British  

noun

1. the ratio of the volume enclosed by the cylinder of an internal-combustion engine at the beginning of the compression stroke to the volume enclosed at the end of it

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Etymology

Origin of compression ratio

First recorded in 1905–10

Example Sentences

Formula 1's governing body the FIA said on Saturday that a change to the way the compression ratio was measured would be introduced on 1 June, with a further revision for the 2027 season.

From BBC • Feb. 28, 2026

Off track, one of the main focuses of pre-season has been a row between the engine manufacturers over the rules governing the engines' compression ratio.

From BBC • Feb. 20, 2026

Audi, Honda and Ferrari fear Mercedes have found a way to use thermal expansion and materials technology to exceed the mandated compression ratio.

From BBC • Feb. 18, 2026

And it's not only on compression ratio, but on other things too.

From BBC • Feb. 2, 2026

For instance, an engine with a compression ratio of one-third has an air-standard efficiency of 0.36, and the actual indicated efficiency of a well-designed engine should be .36 multiplied by .7 = 0.25.

From Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 4 "G" to "Gaskell, Elizabeth" by Various