Bore And Stroke

An engine with a larger bore than stroke is called oversquare and tends to rev more freely. An engine with a longer stroke than bore is undersquare and tends to produce strong low-speed torque. Both values are listed in technical data in millimetres.

Displacement per cylinder equals the area of the bore multiplied by the stroke, and the total is multiplied by the number of cylinders.

Reboring an engine increases the bore slightly and needs matching oversize pistons. Changing the stroke requires a different crankshaft and is a major modification.