What is over square Engine?

An "oversquare engine" is an internal combustion engine where the bore (diameter of the cylinder) is larger than the stroke (the distance the piston travels). The opposite is an "undersquare engine". A square engine has a bore equal to the stroke.

Oversquare engines tend to rev higher and produce more power at higher RPMs due to their shorter stroke. This is because the shorter stroke allows for faster piston speeds before reaching damaging inertia forces. However, they generally produce less torque at lower RPMs compared to undersquare engines.