Bore, Stroke & Displacement Calculator
The number cast into the case is a claim, not a measurement — and on an unbadged engine there is often no number at all. Bore and stroke are the two figures you can take yourself, and together they settle the argument: true displacement, the class the engine was sold as, and whether somebody has already been inside it with a big-bore kit.
Measure the cylinder across its widest point, not the piston.
Crown at top dead centre down to crown at the bottom, or twice the crank throw.
Chamber, gasket and deck volume, filled from a burette. Leave it blank to skip compression.