The part to consider though is that the rod then has to be decelerated to stop and reverse which "returns" that energy. If you look at rod failures it has been determined, barring a contributing factor, that rods usually fail in tensile stress, essentially pulled apart, usually on the exhaust stroke, (decelerating) while "pulling" on the crankshaft.

 

OK, so nobody wanted the simple answer!

Then add in the effect of a longer vs shorter stroke.

 

Pick me! pick me!

Um, lets see, since the flywheels are bigger on a longer stroke motor, there is more mass on the rotating assembly. Which means on the longer stroke motor, more energy is stored in and returned from the rotating assembly. So you have more to gain by lightening the flywheel and rods on the stroker motor...

Its also important that this added mass on a larger diameter flywheel is further away from the center of rotation. The further the weight reduction is from the center of rotation is, the more difference it makes. So taking 1oz off the outside edge of a long stroke flywheel helps more than taking 1oz off the outside diameter of the shorter stroke (small) flywheel.

I saw a tech sheet from a lightweight crank manufacturer slamming other companies because they took all the weight from the center of the shaft. Which doesnt make nearly as much difference as taking the weight from the balancers. Same weight, not as much benefit

 

A+

But I thought someone would go ahead into rod angle and piston speed.

 

Then discuss the dwell time of the piston at TDC based on stroke, rod length and head configuration and effect on cylinder fill...

 

 

I consider myself to be "above average" in engine and physics knowledge, and I understand what you're describing... that the geometry of the rotating mass effects the dwell time of the piston. The time that the piston is "still" effects the intake of air because there is no vacuum pulling it in for that moment...

but im still not touching this one with a ten foot pole (even though I kind of grazed it already lol)

 

Well, in my simple thinking it would work like this...
Heavier rods would take more energy to get moving, therefore using up available horsepower, but once moving it would have more kinetic energy which would translate to more torque?
Simple man's thinking here, but more weight of internal moving parts would result in less hp but more tq....? Kind of like a diesel engine....most huge diesel engines don't make a great amount of hp, but have amazing tq numbers.

I may be way off base here, but it makes sense to me.

 

A good article and well worth reading. Thanks.

 

So if you want some change, get rid of that heavy 300 rear tire, use lighter wheels and feel the acceleration...