Engine Compression Ratio Calculator
Calculate the static geometric compression ratio from swept and total clearance volumes per cylinder.
Formula
CR = VBDC / VTDC = (Vs + Vc) / Vc
Swept volume Vs: 500 mL · Net clearance volume Vc: 50 mL · Compression ratio (to 1) ≈ ((500 mL × 0.001 L/mL)+(50 mL × 0.001 L/mL))÷(50 mL × 0.001 L/mL)
How to use
- Enter the swept volume of one cylinder.
- Enter its net clearance volume at top dead center.
- Read the ratio; a result of 11 means 11:1.
Examples
- 500 mL swept and 50 mL clearance give 11:1.
Frequently asked questions
What belongs in clearance volume?
Use the total space at TDC, including chamber, compressed gasket, deck clearance and the signed piston dish or dome correction.
Does cylinder count change the ratio?
No. Use volumes for the same cylinder, or matching totals across identical cylinders.
Is this dynamic compression?
No. Static volume ratio does not account for valve timing, boost, leakage or pressure measurements.
Sources
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