M20 wide box

[novadude]

I don't think M21s have any place in a street car these days. The ratio "spread" from 1-2, 2-3 is exactly the same on an M20 vs M21. M20 just has a wider ratio spread on the 3-4. Seems to me that M20s are a more practical choice if you are not racing and can afford the greater 3-4 rpm drop.

You can run a taller axle and still have the same "feel" in 1-2-3 gears. A 3.31 gear behind a M20 will have the exact same final drive ratio in 1st, 2nd, 3rd as a M21 with a 3.79 gear (3.73 if you want to talk about "real" ratios).