Mean piston speed

As the alloy tends to be fairly consistent across most manufacturers, the maximum velocity of the piston at a given rpm is determined by the length of the stroke, that is, the radius of the journal of the crankshaft.

The opposite, oversquare, is mostly used in higher performance engines where the torque curve approaches the peak of the maximum piston velocity.

Generally in this type of engine, the volume of the cylinder can be artificially enhanced with turbochargers or superchargers, increasing the amount of fuel/air available for combustion.

The cylinder diameter in these engines are fairly small (under 45 mm) and the stroke is less than that, depending on the torque curve and maximum available rpm as designed by the builder.

Up until the early 1960s, the focus by designers was on torque rather than piston velocity, probably due to material considerations and machining technologies.