Static compression ratio from your engine geometry — plus effective CR under boost.
Bore, stroke and the total clearance volume per cylinder (chamber + gasket + deck + dome/dish).
Static CR = (swept volume + clearance) ÷ clearance.
Optionally enter boost to estimate the effective compression ratio for a forced-induction build.
CR = (Vd + Vc) ÷ Vc, where Vd is the swept volume of one cylinder (π/4 × bore² × stroke) and Vc is the total clearance volume per cylinder.
It approximates the static CR multiplied by the manifold pressure ratio: CR × (1 + boost_bar ÷ 1.013). It is a rough guide to detonation risk, not an exact thermodynamic figure.
Lower static CR (typically 8.5–9.5:1) is common for high-boost petrol builds; higher static CR can work on E85 or with conservative boost and good fuel/knock control.
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