Stroke to Bore Ratio

The stroke is compared with the bore. This stroke-bore ratio has influence on the operational behaviour of the engine. While the shortstroke engine (picture left) has less stroke than bore, this is with the longstroke engine (picture right) turned around. If both are approximately alike, then one speaks of an oversquare engine.

While longstroke engines rather benefit from their torque in the lower speed range, shortstroke engines are rather capable of a particularly high revolution numbers level and large valve openings. Extreme example is the current (2007) formula 1 with 2,4 Liter-V8 and about 98 mm bore and 40 mm stroke.
The latter ensures for the fact that the middle piston velocity rises despite a maximum speed of 19.000 1/min average piston velocity not substantially more than 25 m/s. In order to keep the weight of the pistons small, there is no oil wiper ring, nearly no piston shaft and a piston pin, which are strongly shortened directly attached under the piston crown.