Dntmn,


The term, or should I say, buzz-word, 'Long Stroke' went out with flared slacks and elevator shoes...

An under-square (i.e. long-stroke) engine does not produce more torque than an over-square engine.

Ring drag is a negligible factor and it is about the only thing, which is lower in an under-square engine that could contribute to torque.

With given event-timing (port opening numbers in degrees), an over-square (short-stroke) engine will have larger port openings, which will allow a more complete exhaust scavenging and a better cylinder filling, compared to an under-square engine.


With a given displacement, the under-square engine will have a longer stroke, for more leverage, but also a smaller diameter piston, which results in a lower combustion force, so no torque improvement will result.


Back to glow engines; some of the engines considered 'torque paragons' like the MVVS .91, are over-square, short stroke engines.

If an engine is designed with a longer stroke, the engineer would typically time it for spinning a larger prop at lower RPM, to prevent excessive piston speeds. So it will readily spin larger props at lower RPM numbers and at this lower RPM regime, it will have an advantage, but it is very unlikely to have an absolute torque advantage, compared to a similar, over-square engine.


Most engines are very close to being square anyway.