Engine geometry / 01
Compression ratio.
Your measurements. The full volume breakdown.
Static ratio and displacement, in metric units.
Static compression ratio
- Engine displacement
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- Swept volume / cylinder
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- Clearance at TDC / cylinder
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- Head chamber
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- Head gasket
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- Deck volume
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- Piston crown contribution
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Geometric calculation only. Not a fuel, tuning or engine safety recommendation.
Behind the numbers.
Use measurements from your own engine. The example is illustrative and does not represent a manufacturer’s specification.
Swept volume = π × bore² × stroke ÷ 4 ÷ 1,000
Compression ratio = (swept + clearance) ÷ clearanceDimensions are in millimetres and volumes in cubic centimetres (cc). Component mode adds the head chamber, compressed gasket, deck and piston crown contributions to find clearance at TDC. A dish adds volume; a dome subtracts it.
This is the full-stroke, static ratio. Two-stroke trapped compression ratio requires exhaust-port timing and is not calculated here. It also does not account for valve timing or dynamic compression.
Formula reference: JE Pistons compression calculator ↗