Compression ratio

Description

The compression ratio of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity. It is a fundamental specification for many common combustion engines. In a piston engine, it is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke, and the volume of the combustion chamber when the piston is at the top of its stroke. The ratio is calculated by the cylinder bore (diameter), the piston stroke length and the clearance volume that is the volume of the combustion chamber (including head gasket).

Related formulas

Variables

CRCompression ratio (dimensionless)
πpi
bThe cylinder bore (diameter) (in)
sThe piston stroke length (in)
VcThe clearance volume ( the minimum volume of the space at the end of the compression stroke) (in3)