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Static Compression Ratio Calculator

Calculate static compression ratio from bore, stroke, chamber, piston volume, gasket and deck clearance.

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Calculator

mm
mm
cc
cc; enter a dome as a negative volume
mm
mm
mm. Positive = piston below deck; negative = above deck.
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How the calculation works

Static compression ratio is (swept volume + clearance volume) ÷ clearance volume. Clearance volume includes chamber volume, piston dish/dome contribution, head-gasket volume and deck-clearance volume. Every input needs the same sign convention to avoid a believable but wrong answer.

Measurements matter. Catalog piston dome/dish values, resurfacing, gasket compressed thickness and actual chamber volume can all change the result. For a rebuild, use the exact component data and measured engine geometry rather than a generic engine-family number.

Worked example

Changing only gasket thickness changes clearance volume in every cylinder and therefore the static ratio. The calculator makes that geometry visible, but it does not tell you whether a particular ratio is appropriate for your fuel, camshaft, combustion chamber or boost target.

Important limitations

Static compression ratio is not a safe-boost calculator. Detonation margin depends on fuel octane/ethanol content, intake temperature, chamber design, cam timing, ignition timing, charge motion, cylinder pressure and calibration. Engine-machine work should be verified by the builder doing the measurements.