Engine Compression Calculator
Compute the theoretical compression ratio of an engine from bore, stroke and combustion chamber volume.
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Compression ratio basics
Compression ratio = (swept volume + clearance volume) ÷ clearance volume. It tells how much the fuel-air charge is squeezed before ignition.
- Typical petrol engines : 9.0:1 to 12.5:1
- Turbo petrol engines : 8.5:1 to 10.5:1 (boost needs lower static ratio)
- Diesels : 16:1 to 22:1
- Higher ratio = more efficiency and torque, but requires higher-octane fuel
FAQ
Yes, by skimming the head or using thinner gaskets or higher pistons, but you must respect fuel octane, valve clearance and piston-to-valve clearance. Beyond a point you get knocking.
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