Your true static compression ratio from the parts you actually have: chamber, piston, deck, and gasket. No guessing from a catalog description.
Compression ratio is (swept + clearance) ÷ clearance. On a 350, swept volume is about 717 cc and clearance is only about 78 cc, so a 5 cc change anywhere, a different gasket, a deck cut, a dish, moves the ratio by roughly half a point. Catalog ratios assume catalog parts.
Deck height plus gasket thickness is your quench distance. Tight quench (around 0.035 to 0.045 inch total) fights detonation; a thick gasket used to drop compression also opens the quench up, which can make the detonation problem worse, not better.
Head castings vary, and milling history is invisible. A burette and a few minutes per chamber tells you the real number. The same goes for deck height: measure all four corners before you order pistons around a guess.
With flat-top pistons, a 0.025 inch deck, and a 0.039 inch gasket, about 10.2:1. Change to a typical 12cc dished piston and the same engine drops to roughly 9.4:1. Both combos are presettable above: the defaults show the flat-top version.
Noticeably. On a small-block, going from a 0.039 to a 0.051 inch gasket adds about 2.6 cc of clearance volume and drops the ratio by roughly 0.3. It also widens quench, which can hurt detonation resistance, so it is a tradeoff, not a free fix.
Both. Static is the mechanical ratio this page calculates. Dynamic accounts for the intake valve closing after bottom dead center, which bleeds cylinder pressure at low RPM. A big cam can make a 10.5:1 engine behave like 9:1 at cranking speeds, which is how race-cammed engines survive on pump gas.
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This compression ratio calculator is one of 11 free tools in the Pistons & Ink Digital Toolbox, built for the aftermarket auto industry. If it helped you, the rest of the toolbox is right here.
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