Compression Ratio Calculator

Compression ratio is the swept volume plus the clearance volume divided by the clearance volume, so it needs every space left above the piston at top dead centre. Enter bore, stroke, the measured chamber volume, the gasket bore and compressed thickness, the deck clearance and the piston dish or dome, and the tool adds those volumes up and returns the static ratio with the four pieces shown separately. A second mode takes that static ratio with the rod length and the intake valve closing angle and gives the dynamic ratio, which is lower because the valve shuts after bottom dead centre. The chamber figure has to be measured rather than taken from a catalogue. A ratio on its own does not choose a fuel, because cam timing, chamber shape and cooling all move what an engine will tolerate.