Enter the cylinder bore diameter, stroke length, and the minimum clearance at end of the compression stroke. The calculator will evaluate and display the compression ratio of the engine.
Compression Ratio Formula
The following formula can be used to calculate the compression ratio of an engine.
CR = [ (PI/4*b^2*s) + Vc ]/Vc
- Where CR is the compression ratio
- b is the cylinder bore diameter
- s is the stroke length
- Vs is the minimum clearance at the end of the compression stroke
Compression Ratio Definition
A compression ratio is defined as the ratio of total working volume to total compression volume.
Compression Ratio Example
How to calculate compression ratio
- First, measure the bore cylinder diameter
This should be the inner diameter of the cylinder, not the outer diameter.
- Next, measure the stroke length
Measure the stroke length of the cylinder.
- Next, determine the minimum clearance
It’s important that the minimum clearance is the clearance when the compression stroke is at its highest point.
- Calculate the compression ratio
Enter the information from steps 1-3 into the equation above to calculate the compression ratio.
A compression ratio is a fundamental specification in combustion engine design that measures the ratio of the total working volume of a piston and its compression volume.
The higher the compression ratio the better the performance of a piston. The more compression the fuel undergoes, the more pressure it sees, and the higher the thermal efficiency of the engine.
Thermal efficiency is the total mechanical energy that can be extracted from a set amount of fuel.