An engine where the ratio of
bore diameter:
stroke length is less than 1.0
is referred to as undersquare. Generally undersquare engines operate at higher
torque and lower
RPM.
The use of larger stroke limits the RPM of the engine for two reasons, first
the total speed of the piston has a practical limit, second the burning
of the fuel mixture proceeds at a fixed rate, and the use of a longer
stroke dictates that at high RPM, the fuel cannot be fully burned in a larger
cylinder.
Most engines manufactured before WWII were of undersquare design. Undersquare
engines have their advantages, however they tend to be heavy and use more
fuel than more modern designs.