Effective compression calculator
See effective compression and pressure ratio from your static CR + boost.
Approximation using sea-level atmospheric pressure (14.7 psi). Real detonation margin also depends on IAT, chamber design, and fuel — this is a planning aid, not a tune.
Why effective compression matters
Boost raises cylinder pressure, so a boosted engine behaves like a much higher-compression one. Effective CR ≈ static CR × (boost + 14.7) ÷ 14.7. A 9.5:1 engine at 8 psi acts like roughly 14:1 — which is why pump-gas boost demands richer fueling and conservative timing, and why higher-static-compression motors knock sooner under boost.
This uses sea-level atmospheric pressure; real knock margin also depends on intake air temp, fuel octane, and chamber design. It's a planning aid, not a tune — verify fueling with a wideband and keep timing conservative before adding boost.