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Static Compression Ratio Calculator

Calculate the static compression ratio for your engine build. Input cylinder volume, piston displacement, head gasket thickness, and other specifications to determine your compression ratio.

Precise calculations No data stored Mobile friendly
10.5:1 Typical Ratio

Static Compression Calculator

Units

Engine Specifications

Diameter of the cylinder
Distance piston travels from TDC to BDC
Length of the connecting rod
Height of the piston from wrist pin to top

Combustion Chamber & Gasket

Volume of the cylinder head combustion chamber
Compressed thickness of the head gasket
Diameter of the head gasket opening

Piston Specifications

Positive for dish, negative for dome
Distance piston is below deck at TDC
Volume of ring lands and grooves

What is Static Compression Ratio?

The static compression ratio is the ratio of the total cylinder volume when the piston is at bottom dead center (BDC) to the volume when the piston is at top dead center (TDC). This is calculated without considering cam timing.

Formula: CR = (Swept Volume + Clearance Volume) / Clearance Volume

Typical Compression Ratios

Compression ratios vary by engine type and fuel requirements. Higher compression ratios generally produce more power but may require higher octane fuel.

Ranges: 8:1 (low) to 13:1 (high performance)

Important Considerations

Static compression ratio doesn't account for cam timing. For more accurate results, also calculate dynamic compression ratio which considers when the intake valve closes.

Note: Dynamic CR is typically 1-2 points lower

Fuel Requirements

Higher compression ratios require higher octane fuel to prevent detonation. Always verify fuel requirements for your specific engine combination.

Guideline: 10:1+ may need premium fuel

Engine Building Tips

Accurate Measurements

Use precise measurements for bore, stroke, and chamber volumes. Small errors can significantly affect compression ratio calculations.

Cam Timing

Consider cam timing when planning your build. Aggressive cams can reduce dynamic compression even with high static ratios.

Heat Management

Higher compression generates more heat. Ensure proper cooling and consider thermal management in your build.

Build Verification

Always verify your compression ratio with actual measurements after assembly. Use a burette for accurate chamber volume measurement.