In 4-strokes, the whole long stroke=high torque myth reverses cause and effect. Long stroke engines had good low rpm torque because they were tuned that way - that in turn was because the long stroke mechanical forces combined with the smaller valves due to small bore prevented them from revving, so tuning for low rpm grunt made sense. And a lot of that goes back to British tax law, which based taxes only on bore, not displacement, so naturally they made silly long stroke engines. Other things like poor lubricants and good valve trains made high rpm a difficult design problem too.I just can't resist. It take compression to make RPM=Power.Lower compression longer stroke slower RPM makes torque plane and simple. My O41 is a prime example.This saw has145lbs of compression is a slower RPM than say my 51 but pulls a 20BC with ease.Like comparing a 390 ford to a 327 Chevrolet.Ken
It's true that longer crank arms give better leverage, but if you look at an cylinder as a pneumatic piston, a bigger bore means more piston area and more force.