Bore is the diameter of each cylinder and stroke is the length that it travels when moving from bottom position to the top position. Engines with the bore bigger than stroke are called oversquare engines, with the bore smaller than stroke are called undersquare engines and exactly equal are called square engines.
Oversquare engines allow bigger or multiple valves in the head and have less loss to friction due to the shorter stroke, but are only efficient at higher revs thus are more typical in high performance engines, like in your example for a sport bike. Bigger engines also have a larger bore even in trucks to limit the length of the stroke, thus limiting losses of the pistons rubbing the rings.
Undersquare engines allow for a better torque in low revolutions where the longer stroke will not affect performance so much but the fuel burn will be more efficient due to the lower volume when the air/fuel mixture is compressed, leading also to lower fuel consumption. Diesel engines also are massively undersquare engines (typically around 3:1 ratio) since those engines have a very high compression ratio compared to gas engines (around 22:1 ratio).
#OverSquare #UnderSquare #Engine
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