How to Calculate Engine Compression

The compression of an engine is expressed in a ratio that says how many units of volume from the cylinder with the piston at the bottom dead center are squeezed into a unit of space in the compression area with the piston at the top dead center. For example, if five units are being compressed into one unit of space the compression ratio is 5.0:1. The compression ratio is affected by the clearance volume, piston dome, cylinder swept volume, chamber volume and head gasket volume (see Resources).

Things You'll Need

• Calculator

Instructions

1. Add the cylinder volume to the clearance volume.

2. Add the piston compression volume to the sum from Step 1.

3. Add the head gasket volume to the sum from Step 2.

4. Add the chamber volume to the sum from Step 3. Set this sum aside.

5. Add the clearance volume to the piston volume.

6. Add the head gasket volume to the sum from Step 5.

7. Add the chamber volume to the sum from Step 6.

8. Divide the sum from Step 4 by the sum from Step 7. This is the compression ratio.

Resources

• Engine Compression Calculator