[mbeeman400]

The PO of my 70 Trans Am RA lll replaced the worn out 3.55 with a 3.08 in a 12 bolt rear. So with a 2.52 first gear Muncie , take offs are not great. So can I go back to a 3.55 or 3.73 with my current carrier?
Also looking for gear manufacturers recommendations! Thanks in Advance

[Squidward]

Yes. The next carrier break starts at 3.90, so you would be good with your existing carrier up through 3.73.

[mbeeman400]

Originally Posted by Squidward

Yes. The next carrier break starts at 3.90, so you would be good with your existing carrier up through 3.73.

Thank you!

[locomotivebreath]

It may be easier to replace the M20 with a new M22-z Muncie . It has a 2.98 1st gear to take advantage of the 3.08 . It’s not recommended for much drag strip abuse . I’d be awful tempted to go this route .

[mbeeman400]

Originally Posted by locomotivebreath

It may be easier to replace the M20 with a new M22-z Muncie . It has a 2.98 1st gear to take advantage of the 3.08 . It’s not recommended for much drag strip abuse . I’d be awful tempted to go this route .

Interesting, not up to speed on that. Thanks for the idea! Back to "Google School" LOL

[PDC]

I will second the M-22 ‘Z’ route with the 3.08 rear. I have this set up in my 73 with a mildly built 455 (FT, aluminum D-ports). If you need a stronger trans, look into the M-23 ‘Z’ which is stronger than the M-22 variant. Maybe not ideal for maximizing every 10th at the track due to the bigger drop between gears, but I find the long stroke Pontiac motors have no difficulty pulling easily between the wider spread gears in the ‘Z’ gearset. Your overall gear reduction in 1st gear with the 3.08 and the M22-Z will be around 9.2 - would be even deeper that your current 2.52 1st gear with 3.55s (8.94). But cruising down the highway with 3.55s might make you miss that 3.08 you currently have.

[locomotivebreath]

From a price point , I think the op would come in pretty close to what it’ll take to have a rear done as well . https://www.5speeds.com/newm22.html

[coonhunter70]

You'll miss the 3:08's everytime you hit hwy, IMO

[JUDGE3]

I vote for the 3.73's. iv'e had 3.55's and all the way to the 4.30's and everything in between.

3.73 to me is best.

i'm curious about the highway driving talk. I'm guessing we drive these cars for performance not loading up the trunk for a long vacation drive.


if you want long range highway driving do it with the transmission.

[The Champ]

I had 3.42's in my GTO 12 bolt. Swapped to 3.08's after I put in the 462 to make the car more suitable for longer periods of Interstate driving. My Muncie M20 has the 2.56 1st gear. With the 3.42's I had an effective first gear ratio of 8.75, with the 3.08's I dropped to 7.88.

I figured if I didn't like the drop in acceleration from a dead stop, I'd go with the M22Z which would get me to a 9.17 effective first gear.

I will probably do that eventually, but the 9% drop in effective 1st gear ratio wasn't that big a difference with the 462 that replaced the original 389.

For the OP, putting in an M22Z will give you an effective first gear as if you had a 3.64 rear gear, yet keep your highway RPM's at under 2700. Assuming you could buy 3.64 gears, you'd be spinning close to 3200 RPM with 27" tall tires.

[TedRamAirII]

I would get the M22Z. I dont know if there is such a thing as a M23Z? I would think the M22Z would be fine for street use, but when cars find traction, that's when things break. I dont know if the M22Z is "weak". Paul would be the one to answer question on that. http://5speeds.com/

[locomotivebreath]

I don’t think that it’s weak , but not designed to do a hole shot .The web sight says not recommended for repeated drag strip use so I guess some common sense should be used . Sounds more like a trans for some big performance street and that would suit most of us I think .

[Formulajones]

I don't care for the M22Z route personally. It's nothing but a 4 speed with steep first gear and a wide gear spread to boot. If it can't tolerate a few hole shots it's just not going to work for me. Plus they are way too expensive for what they are. $2200+ for a 4 speed?? That's damn near 5 speed territory. May as well just run a ST-10 with a 2.64 or 2.88 first gear and essentially do the same thing for half the cost.

I agree with Judge3, I find a car is a much better all around performer that does both things very well if you just attack this with the transmission (meaning overdrive) rather than monkey with 1st gear ratios in a 4 speed and then band aide highway driving with the rear gear.

I like driving my cars (drive them daily) but we also frequent the track for fun time, that's what these cars were built for. Finding the best of both isn't going to happen with a standard 1:1 trans. There are compromises.

If I were you mbeeman400, I'd go back to the 3.55's, leave the M20 and enjoy the car that way for a while, and if you feel the need for a change, attack it at the transmission with an overdrive. Could even cushion it a bit with a taller rear tire if you want.

One of our daily drivers is an M20 with 3.55's. For 2 years we've been everywhere in it, 300 mile Rt 66 cruises, my wife drives it to work every day, family outings on the weekends. Not a big deal. If this is just a fun weekend car for you, I'd toss in the 3.55's and leave it alone.

[Region Warrior]

I start from the rear and work forward.
Largest circumference/widest tire can fit w/o rubbing. Then chose rear gear to match final trans ratio so engine rpm is in mid power band at cruising speed.
RPM doesn't worry me as much as lugging the engine.
Plus power response is usually good at all speeds....

[locomotivebreath]

Do you mean peak torque or half way through the torque band when you say mid power ? Cars with cvt transmissions aim to keep the engine at or near peak torque , which will keep the rpm deceptively high yet deliver impressive mpg . At least that’s how my Nissan work beater was until it lunched the cvt !

[The Champ]

Originally Posted by TedRamAirII

I would get the M22Z. I dont know if there is such a thing as a M23Z? I would think the M22Z would be fine for street use, but when cars find traction, that's when things break. I dont know if the M22Z is "weak". Paul would be the one to answer question on that. http://5speeds.com/

The Autogear M22Z is much stronger than the original M20 and is based on the M22 Muncie Rock Crusher.. It has the Autogear Muncie Super Case for even more strength than the original M22.

https://www.midwestmuncie.com/produc...ear-end-gears/

The M23Z does exist and is about a $200 - 300 upgrade for those so inclined.

https://www.midwestmuncie.com/product/super-duty-m23/