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Dynamic Compression Calculator
Calculate dynamic compression with your cam timing
Dynamic compression ratio is the effective compression after the intake valve actually closes — the ratio the engine feels at low RPM.
Formula: Effective stroke from slider-crank geometry at the intake closing point; DCR = (effective swept + clearance) ÷ clearance
What this number means
This calculates dynamic compression ratio by accounting for where the intake valve actually closes, which is when the cylinder truly starts compressing. Two engines with identical static ratios can have very different dynamic ratios because of cam timing.
What to change next
If dynamic compression is high for your fuel, a later-closing intake cam can tame it without changing pistons — and vice versa for a lazy, low-dynamic combination. Use it to match cam and pistons as a pair, not separately.
Worked example
A 10.24:1 static small-block (4.030 bore, 3.48 stroke, 64 cc chambers) with 5.7 in rods and an intake valve closing at 62° ABDC gives a dynamic ratio of ≈ 8.35:1.