I'm thinking stick with the M20 for the lower (numerically higher) 1st gear, mainly because of your 3.08 rear gears. But I haven't given your tire diameter any consideration.

I would think the 21 with the 308 would be an easier driving off the line choice. Not that hard to swap out just to try.

4SPEED427 wrote:

---

70 SS ACADIAN wrote:

---

I would think the 21 with the 308 would be an easier driving off the line choice. Not that hard to swap out just to try.

---

 It's a 2:20 first gear vs the 2.56 Kevin. Unless you use extra rpm it's tougher to launch

But you're right, that's the nice thing about a Muncie, the swap is simple.

---

 There you go, I learned something. I was thinking the 21 had the lower 1st gear. I guess an old guy like me should stick to a power glide

If I step on the gas too hard it spins the tires with ease and seems to pull well in every gear. But I am curious to find out the difference between the two.
You are right Kevin, it is an easy swap, if I can change the clutch in less than three hours the trans swap should be quicker. Since concrete does not set well in these freezing temperatures and I am getting another day off tomorrow, maybe I will change it. And I a week or two the roads will be dry enough to test it out.

torque is key.

my knee-jerk reaction after reading 3.08:1 was that I'd stay away from a 2.20 first gear, because it will be far from ideal.

I am unaware of any division ever putting less than a 3.42:1 behind a M21/M22 ever.
Even with 3.42:1 & 2.20 first, you're looking at a far from ideal 7.524 effective first gear ratio.
Your current (with a 2.56 1st?; most have a 2.52) effective first gear ratio is 7.88, but swapping in the M21 will put your effective first gear at a paltry 6.776.

I used to have a 3.55:1 behind my M22, and I knew it was less than ideal, and for the most part it was fine to drive.
My brother currently has a 3.08:1 behind my old M22 in his car (it's only there temporarily till he can setup another rear with 3.42:1 or better), you definitely have to feather the clutch and gas when starting off...

If you have Buick realm torque, I'd say go for it;
If you feel like swapping transmissions back and forth to see if you like it, go ahead.
I'm guessing you won't like it.

-- Edited by unruhjonny on Tuesday 21st of January 2020 02:18:54 PM

After considering all who have given there advice on the site and a few local car guys I am not going to change transmissions. Aaarg, I need to get back work and leave the car alone, its working fine. Maybe I should get back to taking the dents and scratches out of the extra spinner caps laying around. Thanks to all who chimed in.