Originally Posted by Slapz
How much HP will a Muncie 4 speed hold. How do you distinguish between an M21 and an M22. The M22 is what they called the "rockcrusher" right? Is that the better trans. Want to put this behind a 648 hp blower motor, My gramma drives an auto, I just want to have fun!
A stock Muncie- even the fabled 'Rockcrusher'- will not last long behind that much hp, at least not if there's any traction involved.
There ARE aftermarket parts available to make a Muncie strong enough to deal w/it, and there are other trannys altogether that might be a better choice like a Tremec 6-speed (RPM Performance, Finishline Transmission, The GearBox, D&D Performance have been mentioned on this board for Tremec 6-speed performance builds).
I'll leave it to AutoGear and any other members that may have more info for you on this.
Input shaft rings and other clues can help to determine a close ratio from a wide ratio from a 'crusher, but the best way to tell is to pull the side cover to see exactly what you have- gears can and often are changed during the life of a transmission, especially one as old as the Muncie. You can google "muncie identification" and get more info.