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

From 1 June, the compression ratio will be measured at 130C as well as ambient temperature, and from next year only at 130C.

From BBC • Feb. 28, 2026

Audi's entry this year rekindles that old rivalry with Mercedes, and battle lines have already been drawn in a pre-season row over the rules governing the engines' compression ratio.

From BBC • Feb. 27, 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

Audi, Honda and Ferrari fear Mercedes have found a way to exploit the way materials expand with heat to have the engines running to a higher compression ratio when the car is on track.

From BBC • Feb. 9, 2026

Taking r = 5, as before, for the compression ratio, the possible efficiency is reduced from 48% to 38%, if γ = 1.29 instead of 1.41.

From Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 2 "Hearing" to "Helmond" by Various