Automotive Tools
Engine Math
Static Compression Ratio
Compute static compression ratio from bore, stroke, chamber volume, piston dish/dome, and head gasket thickness.
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How to Use This Tool
- Enter bore and stroke in mm or inches.
- Add head chamber volume (cc) and piston dish (positive) or dome (negative).
- Set gasket thickness and gasket bore (often slightly larger than cylinder bore).
- Include deck clearance if the piston sits below or above the deck.
The Formula & Physics Behind the Math
Swept volume = π/4 × bore² × stroke. Clearance volume = chamber + gasket volume + deck volume + piston dish/dome. Static CR = (swept + clearance) ÷ clearance. Dish adds volume (higher CR drop); dome subtracts volume.
Frequently Asked Questions
Is this dynamic compression ratio?
No — this is static CR only. Dynamic CR also needs intake valve closing point and cam timing.
How do I enter a domed piston?
Use a negative number for dome volume (e.g. −8 cc). Dish pistons use a positive value.
What about quench?
Quench is gasket thickness + deck clearance. Keep it within your builder’s recommended range for detonation control.