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.

---

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

---

Etymology

Origin of compression ratio

First recorded in 1905–10

Example Sentences

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

The compression ratio is a measurement of the cylinder displacement between the two extremes of the piston stroke.

From BBC • Feb. 18, 2026

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

From BBC • Feb. 2, 2026

That is, 104 pounds per square inch is the most efficient final compression pressure to have for this engine at sea level, since it comes directly from the compression ratio.

From Aviation Engines Design?Construction?Operation and Repair by Pag?, Victor Wilfred