[mhintz]

What is the difference between the M20 and the M21 transmission?

 

[riskyvt]

In general, just the gear ratios. M20 had a more aggressive 1st gear ratio, M21 was less. If you plan to use one vs. the other, make sure you take your rear axle gear ratio into consideration.

Here's a good reference site for your education on Muncie's: http://www.5speeds.com/muncie.htm

 

[David Bates]

The only difference between an M20 and an M21 parts wise are the input gear and cluster. Everything else is the same.

 

[Guest]

The only difference in the two is the input and the cluster, all other gears are the same.

Standard M20 is a 2.52 low gear, M21 is 2.20 low. The super early M20, 63/65 have a 2.54 low gear.