Crankwalk really has nothing to do with how high the motor revs. Biggest cause for it is extremely strong pressure plate. Theoritically there is no front to back force from the piston motion. In the real world its extremely small. Biggest problem internally with the M series motor is that all the rotating parts are extremely heavy. I hate to say it, but if you want to see a good example of a high output NA motor look inside a Honda. Their engines are pretty much textbook examples on what to do.