Enter your engine's Bore, Stroke, Head Volume, Deck Clearance, Gasket Thickness, Piston Dome/Dish Volume, and Cylinder Count into the Compression Ratio Calculator to find your Static Compression Ratio, Total Displacement, Swept Volume, and Clearance Volume.
Static Compression Ratio
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Total Displacement
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Swept Volume (per cylinder)
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Clearance Volume
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Compression ratio is the ratio of the cylinder volume when the piston is at bottom dead center to the volume when at top dead center. Higher compression ratios generally produce more power but require higher octane fuel to prevent engine knock.
Static compression ratio is calculated based on geometric measurements, while dynamic compression ratio accounts for valve timing and when the intake valve actually closes. This calculator provides static compression ratio.
Use a dial indicator or depth micrometer to measure the distance from the top of the cylinder bore to the piston crown when the piston is at top dead center. This measurement is critical for accurate compression ratio calculations.
Use negative values for domed pistons (they reduce chamber volume) and positive values for dished pistons (they increase chamber volume). Flat-top pistons would be 0.
For pump gas (91-93 octane), most engines run best with compression ratios between 9:1 and 11:1. Higher ratios may require race fuel or careful tuning to avoid detonation.
Thicker head gaskets increase clearance volume, which lowers compression ratio. Even small changes in gasket thickness can noticeably affect the final compression ratio.
While the mathematical formulas are the same, diesel engines typically have much higher compression ratios (14:1 to 23:1) compared to gasoline engines. The calculator works for both engine types.