I wonder why an optimum rpm exists? The only things I can think of are:
Increased Inertial Loads at High Rpm?
Increased Friction at High Rpm?
Varying Disparity Between Piston Speed and Flame Front?
*(I know this set a limit on piston size during WWII @ ~5.5" Bore + Stroke)
Piston Position @ Peak Pressure?
Vibration?
Combustion Gas Dwell Time in Piston
Little Magic Elves Need Time to Do Their Work
Answers are no fun without the reasons.
- LostCause