Engine Compression Ratio Calculator

Enter the engine specifications below to calculate the compression ratio.

Compression Ratio:

 

Total Displacement

  cubic inches
  cubic centimeters
  liters


How to Calculate Engine Compression Ratio

The compression ratio of an engine is the ratio between the swept volume and the compressed volume. In other words, it is the ratio between the volume of the combustion chamber when the piston is at its lowest point when gasses are uncompressed and the volume when it’s at the highest point and the gases are compressed.

A higher compression ratio allows the engine to output more power using the same amount of fuel, making it an important performance metric. Thus, higher compression ratios also allow engines to be more fuel efficient.

To calculate the compression ratio of an engine, use the following formula:
compression ratio = Vd + VcVc

Vd is the displacement volume of the motor, or the volume displaced by the piston from the start to the end of the stroke.

Vc is the clearance volume of the motor, or the remaining space left when the piston is at the end of the stroke.

How to Calculate Displacement

Displacement can be found using this simple formula:
displacement = π4 × b2 × s

b is the bore.

s is the stroke.

This will yield the displacement of a cylinder, so to find the total displacement you’ll need to multiply this by the number of cylinders.

Try out engine displacement calculator to find this.

How to Calculate Clearance Volume

The clearance can be found using the formula:
clearance = c + p + d + g

c is the chamber volume.

p is the volume of the piston dome or dish.

d is the deck volume.

g is the volume of space taken up by the gasket bore, when compressed.

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