M20 vs M21 Transmission
Thread Starter
Team Owner
Joined: Dec 1999
Posts: 26,555
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From: Florida
2021 C2 of the Year Finalist - Modified
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St. Jude Donor '03 thru '26
M20 vs M21 Transmission
How do they differ? :confused:
Melting Slicks
Joined: Feb 1999
Posts: 3,349
Likes: 1
From: Colorado
Re: M20 vs M21 Transmission (Dep)
The gear ratios were a lot different. The M20 wide ratio had a 2.52:1 first gear ratio, which helped the small blocks get off the line better. The big blocks and stronger small blocks didn't need as steep a first gear ratio, so the close ratio transmissions started out with a 2.20:1 first gear. That's pretty tall. That's like starting off in second gear on any modern manual transmission car. But shifting gears would put the engine at the same rpm better, and the gear ratios were better separated for performance driving.
The rock crusher M22 had "straight cut" gears (still helical, but at a shallower angle), and was noisier, but definitely handled much more torque. You can still find M22's at swap meets, and they go for about $1200 to $1400 bucks as far as I've seen. Not too many takers at that price. But I do see them every time I go to a good swap meet.
You could make an M20 or M21 stronger too, (Doug Nash 5-speed as well) if you modified it by removing the synchros. That was done on drag cars a lot.
Yes, your M20/M21 will last with a stroker small block or big block, up to a point. They were optioned on big blocks too. They can handle very decent torque.
The rock crusher M22 had "straight cut" gears (still helical, but at a shallower angle), and was noisier, but definitely handled much more torque. You can still find M22's at swap meets, and they go for about $1200 to $1400 bucks as far as I've seen. Not too many takers at that price. But I do see them every time I go to a good swap meet.
You could make an M20 or M21 stronger too, (Doug Nash 5-speed as well) if you modified it by removing the synchros. That was done on drag cars a lot.
Yes, your M20/M21 will last with a stroker small block or big block, up to a point. They were optioned on big blocks too. They can handle very decent torque.
Melting Slicks
Joined: Apr 2001
Posts: 3,399
Likes: 279
From: Olmsted Falls, Ohio
Re: M20 vs M21 Transmission (OHSIXX)
There were two different 4-speed transmissions used in 1975 made by Borg-Warner.
The M20 was a standard "wide-ratio" 4-speed and was rated at 325 lb-ft of input torque.
1st=2.64
2nd=1.75
3rd=1.34
4th=1.00
The optional M21 and L82 only "close-ratio" 4-speed and was rated at 375 lb-ft of input torque.
1st=2.43
2nd=1.61
3rd=1.23
4th=1.00
The M20 was a standard "wide-ratio" 4-speed and was rated at 325 lb-ft of input torque.
1st=2.64
2nd=1.75
3rd=1.34
4th=1.00
The optional M21 and L82 only "close-ratio" 4-speed and was rated at 375 lb-ft of input torque.
1st=2.43
2nd=1.61
3rd=1.23
4th=1.00
