Compression ratio
The ratio of the cylinder’s maximum volume to its minimum volume during piston movement.
Reviewed 05.10.2026 · Version 2 · Scope: General
How to interpret it
It is expressed as a unitless ratio, for example 10:1. It is a geometric characteristic of the engine; interpreting it requires the context of the design and the fuel specified by the manufacturer.
Example
If the hypothetical maximum and minimum volumes were 500 cm³ and 50 cm³, the ratio would be 10:1.
Why it matters to you
It makes it possible to interpret an engine specification without confusing it with a measured pressure or the overall size of the engine.
Common points of confusion
It is not equivalent to displacement, compression pressure, or turbo boost pressure. It is not an instruction to modify the engine.
Documentary sources
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