If I went with a muncie 4 sp in place of a TH350, which should I use, the M20 or M21? I know differential will determine. I do have 12 bolt but not sure on gearing, so since automatic now are either of Muncie models compatable?

Thanks,

RwS

It depends on your gearing (and tire diameter), and what YOU want out of it...

Both the M20 and M21/M22 have a 1:1 4th gear...

The M21/M22 have a 2.20 first gear, usually intended for 3.55/3.73/4.10/4.56, etc...

The M20 has a 2.52 first gear (earlys have 2.56), usually intended for 2.73, 3.08, 3.31 and 3.55s...

M20s can be used with the 3.73/4.10 and can produce great launches, but for street they can almost be impractical (need to shift very quickly) unless you have really tall tires...

Conversely, the M21/M22 can be used with the higher gears, but the clutch will need to be slipped more to get the car going... With the same overall top gear, IMO its pointless to go this route (unless you have the pieces and not the money)...

The gear spread between 1st/2nd and 2nd/3rd is the same for all M20/M21/M22... 3rd/4th is a bigger drop in the M20...


IMO, if you are mainly cruising the car, the M20 is a good choice. the lower trans gears allow good accelaration with higher differentials gears. Those higher diff gears allow better highway cruising (lower rpm)...

I would imagine that if you had a 350 trans

you likely have 273's in the rear

so an m/20 will work a little better for you

but if you have a bunch of horses under the hood
you need to be a bit careful with that combo