I have a stock M20 on my '70BB which is rated 500ftlbs torque and 390HP gross at the flywheel.

I remember reading a while back that the stock muncie could not handle much more than the 500ftlbs torque.

No doubt, there are some here with a more accurate answer.

 

489.67582lbs.:laughing: :laughing:

 

I was part owner of a '55 Modified that had 575+ hp and 550+ torque. We ran the same M-22 for a year. The internals held together fine but the case eventually cracked from the launches.

The M-22 was pretty strong. The previous M-21 did not fare as wel and ate 2nd gear more than once.

:cheers:

 

And that's hooking up with drag tires I asume. With street tires, I bet it would hold up fine for quite awhile.

 

Tim (TimAT) has the muncie 4spd in his vette behind a 454 700hp motor and has had no problems that i know of.you might send him a pm and ask,but i'm pretty sure thats what he has.


Kevin

 

Like Kevin said-- I've got an M-21 close ratio- In it's life, it's NEVER had the hammer really dropped on it OR had a gear really slammed. The side cover has never been off.

I know of a couple of guys- one broke the case and another one twisted the input shaft. Running decent horsepower, and slicks.

What it'll really take? No idea..

 

My car had the original M20 transmission behind a 502/502 crate motor. I trashed a rear end but that tranny held up while it was in (a couple of years but not many miles). I changed it for Autogear supercase M22. I found some stuff on the internet that said this tranny would take 650 or 700 ft-lbs of torque and was under $2000. Seemed like a bargain and gives me room to grow.

 

I was just at Anehim Gear picking up parts for Darrow. I asked him about the M-22 . He said 400HP safely. Anything above that is borrowed time, depending on how it's used.

 

Stock M22's ran behind lots of factory L88's, and I've always read that with only the addition of headers L88's were 500HP to the flywheel.

A guy I knew had owned an L88 and he said he was always breaking u-joints on that car, but the rest held up.

 

Muncie stats

http://www.gearzone.net/muncie2.htm

 

I ran a 502/502 for 2 years on a 30 year old M20 and it held up.

Here's the specs on the super case I run now. I didn't buy the kit, i bought a complete new transmission from AutoGear. Is anyone else running one of these?

"AGE designed this case to replace the stock unit to allow you to run upwards of 600 horsepower on your classic car and not destroy your numbers matching transmission. In fact, you can replace the entire unit for about the same cost as a complete rebuild with new components, and place your entire original unit on the shelf for safekeeping and never have to worry about damaging it due to the loads imposed by the power available to you with today's engine technology.

Key Features & Benefits
356T6 Aluminum case will handle double the horsepower of the stock unit

Will not flex, leak, or break

Larger front bearing for durability

Straight thread o-ringed fill and magnetic drain plugs

Still looks like a classic muscle car transmission should

Fully interchangeable with OEM case"

www.gearstogo.com

 

Stock m-21/20 Muncie, Chevy used them in the 435HP Vettes, the 560HP L-88 went to the M-22 "rock crusher" (which I have in my 72 LT-1 Vette.) I love the comments about my Vette having a "gear drive" for the camshaft, "no its a REAL M-22 dude". Greg Pickett ran a M-22 Muncie behind one of his late 1970's twin turbo IMSA Vettes and it lived but, the transmission was changed out for new one at each race (turbo motor was around 900-1000HP if I recall correctly.) Your 71 Vette has the Muncie with the "big" mainshaft and TH400 rear yoke so it is able to carry more HP than a early (1970 and earlier) Muncie. Auto Gear sells a great M-22 gearset and even the "wide ratio" M-20 gearset can be purchased with the M-22 shallow helix angle (std Muncie=45 degree gear helix=quiet operation M-22=22.5 degree gear helix=noisy operation but, less HP loss and better strength.)