Quote:
Originally Posted by cokata
I am pretty sure that all high revving engines are oversquare because the bottleneck is piston speed, and because you can fit bigger valves, and at high rpm that makes a big diffrence
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The bottle neck is piston acceleration not piston speed. High piston speed is not necessarily bad, but is often so because it typically entails high piston acceleration.
What he said is correct, shorter strokes tend to lead to lower piston friction. First off when running at the same engine speed the piston speed is lower if the stroke is short. Secondly, if the connecting rod is a similar length to that of a longer stroke engine, the max connecting rod angle is smaller. This means the component of the force transmitted through the connecting rod that is pressing the piston into the cylinder wall is smaller.
Power used to overcome friction = friction coeff * force pushing piston into cylinder wall * piston speed
These two things lead to lower friction in a shorter stroke engine.