what is the maximum power a m21 can handle. just wondering.

There is no magic number. A friend broke more behind a 327 than I did behind a BB. If your car doesn't hook it will probably last forever but if it hooks well the trans may last a very short time.

Well,..they put M-21 Muncie's behind LS-6's (454, 450 hp) in big 'ol heavy Chevelles,...but, they had F-70 x 14 bias-ply tires. If you swapped to 10" inch slicks, I think you'd be at risk.

But good news,..Auto Gear has parts, including a beefed up main case that will hold up to most anything a street motor can offer. Take a look:

http://www.carcraft.com/howto/56399/

http://autogear.net/

I'm running the Autogear Muncie...very pleased!

I've been using M-21's for 35 years. They will take a surprising amount of abuse but, as said, mostly depends on traction. If you're hooking up hard with big slicks, then the M-21 probably won't last long. I most always use street tires and the tranny lasts pretty good.

But if you're banging gears (and who isn't?) then expect the M-21 to need repairing here and there.

Most of the transmission people I have talked to rate the M21 at around 375 ft lbs of torque. That always seemed low to me, but that's what I was told. The commentary of the other guys is correct...how long the tranny will last is predicated on the amount of traction you get at the rear wheels. With street tires you shouldn't have any problems, but put slicks or cheater slicks on the car... your looking at trouble.

If you have wheel hop, you can kill an M22 rated at 450 ft. lbs. of torque.

Regards, Jody