A piston engine is oversquare or shortstroke if its cylinders have a greater bore (width, diameter) than stroke (length of piston travel). This is generally considered to be a positive trait, since a longer stroke means greater friction and a weaker crankshaft. An oversquare engine is generally more reliable, wears less, and can be run at a higher speed; though with the aid of modern technology, the disadvantages of undersquare or longstroke engines have been overcome. In oversquare engines power does not suffer, but low-speed torque does to some degree, since torque is relative to crank throw (distance from the crank center to the crankpin)—the leverage, essentially. An oversquare engine cannot have as high a compression ratio as a similar engine with a much higher stroke ratio, and using the same octane fuel. This causes the oversquare engine to have poorer fuel economy, and somewhat poorer exhaust emissions. Components of a typical, four stroke cycle, DOHC piston engine. ... Bore may refer to: A wave in a river caused by an incoming tide - see tidal bore The diameter of a pipe or tube, or the caliber of a gun The diameter of a cylinder and piston in a piston engine (See also: Stroke) A person who is boring The... Stroke can mean: In medicine, a cerebrovascular accident (or cerebral accident) A sunstroke In writing, a single line without any break such as stroke in graphics or Chinese characters, see stroke order. ... Crankshaft Continental engine marine crankshafts, 1942 Crankshaft is also the name of a comic strip about an old, curmudgeonly bus driver. ... A piston engine is undersquare or longstroke if its cylinders have a smaller bore (width, diameter) than stroke (length of piston travel). ... // Mechanical power In physics, power (symbol: P) is the amount of work W done per unit of time t. ... In physics, torque can be thought of informally as rotational force. Torque is measured in units of newton metres, and its symbol is Ï„. The concept of Torque, also called moment or couple, originated with the work of Archimedes on levers. ... Stroke ratio, bore/stroke ratio and stroke/bore ratio are terms that are used to describe the form of a piston engines cylinder when the piston is at the lowmost point. ...

In the past, oversquare or shortstroke engines had a tendency to overheat, but modern technology has solved this problem. Oversquare engines are lighter and shorter than similar undersquare engines, except for their longer length. As the length is not a large problem, these engine types are highly favored by many manufacturers because of their power and compact size.

See also

• Square engine
• Undersquare