Accurate statement on M-20 being better than 21 & 22's?

Discussion in 'U-shift em' started by STAGE III, Sep 2, 2017.

  1. moleary

    moleary GOD Bless America

    The Italian wide ratio M22 set is interesting as far as the reduction between gears compared to any Muncie factory reductions.

    Italian Wide Ratio gear M22 - 2.56 - 1.75 = 31.64% - 1.37 = 21.71% - 1.00 =27.00%
    Factory Muncie M20 (63-65) -2.56 - 1.91 = 25.39% - 1.48 = 22.51% - 1.00 = 32.43%
    Factory Muncie M20 (66>) -2.52 - 1.88 = 25.40% - 1.46 = 22.34% - 1.00 = 31.51%
    Factory Muncie M21/M22 - 2.20 - 1.64 = 25.45% - 1.28 = 21.95% - 1.00 = 21.88%
    Last edited: Sep 4, 2017
  2. knucklebusted

    knucklebusted Well-Known Member

    The drop in the M21 between any gear is too little for my liking as a cruiser, spirited driver. So, if it 25% between 1-2 and 22% between 2-3 is too close and I often go 1-3, that should be about 42%?

    I would prefer a bigger gap between 2-3 and less between 3-4 in the Italian gears. To me, ideal would be 1-2 33%, 2-3 30%, 3-4 28%. Working backwards from 1:1, that would net the following:

    Ideal Ratio M20W = 1: 2.97, 2: 1.99, 3: 1.39, 4: 1.0

    That would give my 3.08 rear end an effective 9.15 total drive or the equivalent of 3.63 with an M20.
  3. David Hemker

    David Hemker Well-Known Member

    I have been street driving and drag racing my GS 455 4 speed for 26 years. I have used all 3 (M-20, M-21, M-22) in my car with rear gear ratios from 2.56 - 4.11 and several different camshafts from stock to the window rattler as well as a Stage 2 cam.
    I have raced with slicks at various tracks as well as with street tires at the Pure Stock Drags.
    The following may have been hashed over and over again here by others but here is a condensed version of my experiences.

    The M-20 is a great street trans due to the 2.52 1st gear ratio making starts from a dead stop much easier on the clutch and engine. There is a reason that this transmission was never factory installed behind big blocks, it cannot handle the torque produced by them. The M-20 is the weakest of the 3 due to the internal gear sizes. Over the years I have broken/stripped teeth from 5 different M-20's. If you do too many 3000 RPM power shifts to chirp or spin the tires you will strip teeth from the gears. Hard/speed shifting at 5000 RPM + will not be an issue due to the torque falling off and the HP taking over. If most of your usage will be street driving with an occasional NEED FOR SPEED with the resulting hard driving/shifting you should be fine.

    The M-21 is the next strongest one and can handle the torque of the big blocks as evidenced by being used exclusively by Buick behind the big blocks but still be careful on those 3000 RPM power shifts where the big block Buicks make gobs of torque. Yes this one will be a bit harder taking off from a dead stop due to the 2.22 1st gear.

    The M-22 has the same gear ratio's as the M-21 but is definitely the strongest due to the teeth on the gears being cut straighter/at less angle therefore the teeth are thicker.

    If I was going to street drive the car with a window rattler or similar cam I would use the M-20 to help the car get moving from a dead stop. If budget allows I would upgrade the input shaft, counter shaft and 1st gear with new technology components due to their greater strength from 40 plus years of metallurgy improvements.
  4. knucklebusted

    knucklebusted Well-Known Member

    I think the M22W Italian gears are probably stronger than the M21 or M20 since it is straight cut and not helical cut gears.
  5. moleary

    moleary GOD Bless America

    D&L for the Italian set is $600 plus shipping..
  6. jmos4

    jmos4 Well-Known Member


    Autogear M22W, Larry at D&L put mine together 2011 or 2012, still no complaints best upgrade compaired to the 2 worn-out Muncies I had prior.

  7. philbquick

    philbquick Founders Club Member

    I usually buy that stuff from Ed Harnette. He is usually quick to point out forigen junk. It's been over 5 years since I priced this out so prices may have changed some.

    No one said they were changing ALL the gears. I was just changing the cluster and input gears. Why are you changing all those gears? 1st, 2nd and 3rd gears all go through the input gear and the front gear cluster gear, so, if you change those 2 gears you change ALL the ratios.

    Hartnett Ed 4 Speeds in Lansdowne, PA 19050 -
    Oct 26, 2014 - Hartnett Ed 4 Speeds at 242 Pembroke Ave, Lansdowne, PA 19050.
  8. knucklebusted

    knucklebusted Well-Known Member

    I don't think you can go from an M21 to an M22W without changing all the helical cut gears to straight cut gears.
  9. philbquick

    philbquick Founders Club Member

    Correct, I thought the conversation was about going from M20 to M21 or vise versa. Yes, to change to a rock crusher you need to change all the gears, the main shaft and rear housing since it takes the 400 yoke. That would probably cost $1,200 or more. I have heard rumors that there are small yoke M22s but I have never personally seen one.
  10. philbquick

    philbquick Founders Club Member

    BTW, they all have helical gear, the M22 gears are less helical then the M20/21.
  11. knucklebusted

    knucklebusted Well-Known Member

    Mine is a 1971 M21 so it is a large output and fine spline input already.
  12. philbquick

    philbquick Founders Club Member

  13. philbquick

    philbquick Founders Club Member

    Are you sure your transmission is a Muncie and not a Super T-10. Does it have a point at the top middle of the side cover?
  14. knucklebusted

    knucklebusted Well-Known Member

    I cannot say for sure but the car is pretty original and the 1971 up Muncies were fine spline input and large output shaft. It definitely has a very high 1st gear with very little drop between gears. It looks like most GM Super T-10 trannies had a lot lower first gear than mine.
  15. dumbgruntss

    dumbgruntss Member

    This thread saved me from a bunch of stress. Thank you. I have a new M22W and I forgot why I got the W. Glad I did. Hopefully Ill get it in my 69 GS Stage 1 soon.
  16. knucklebusted

    knucklebusted Well-Known Member

    Cool. Report back. I'd love to get the 2.98 first gear M23Z.
  17. 87GN_70GS

    87GN_70GS Well-Known Member

    I have that one. Havent driven it yet tho...
  18. jmos4

    jmos4 Well-Known Member

    Hi again,

    Not sure if its mentioned in any post, but the Autogears M22W is a wide ratio set at a similar helix as the older Muncie M22 which were stronger than the M21 due to the gear being thicker ar the base of the teeth.


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