COMPRESSION & DISPLACEMENT
Bore, stroke, chamber, gasket, deck and piston dish in — displacement and static compression ratio out. See what a head skim or a different gasket does before you order parts, and what your CR means under boost.
Engine dimensions
Combustion chamber
Deck clearance = how far the piston stops below the block deck at TDC. Negative if it protrudes.
Targets & boost
Skim removes chamber volume and raises compression; overbore adds displacement and also raises it slightly.
Both are applied on top of the numbers on the left.
Volume breakdown — per cylinder
CR = (swept volume + clearance volume) ÷ clearance volume.
Clearance volume is everything left above the piston at TDC: chamber + gasket + deck + piston dish (a dome subtracts).
Static CR is geometry only. What the engine actually feels is dynamic compression — set by cam timing, intake
closing point, altitude and boost. Two engines with identical static CR can want completely different fuel.
Measure your chamber and dish by cc'ing them; catalogue figures drift after skims, valve jobs and rebuilds.