Muncie M21 & Rea rGear Ratio Advice Needed !!!!!!

I don't have the answer, but someone on this NG will....I'm wondering the same thing (I have a 383 stroker), what's the best muncie 4 speed/rear end combination?

Terry

Hi Terry, Its funny but a guy with a 72 Camaro with an M22 and 3.90 called my house tonight about a trailer I have for sale in front of my house. Hes a local guy and has just about the same setup Muncie M22 still

Thanks Gary

Gary,

My engine has just been rebuilt, but I don't have it back from my builder yet. I told him I'd go with his recommendation for a trans, he told me the best would be a 'wide ratio' muncie 4 speed. I've looked up some info on the difference between a wide ratio and close ratio, like you said the choice depends on the other gear ratios in the drivetrain.-- Terry

I have a wide ratio Muncie I used to run in a 72 Nova. I can tell you what I didn't like about it. 1st thru 3rd the ratios are nice and close, then there is a big jump between 3rd and 4th. On the wide ratio Muncie's 1, 3, & 4 are roughly the same as 1, 2, & 3 on an old 3 speed. They just added another gear half way between 1st and 2nd. I personaly prefer an even spread all the way through. Have you concidered using a Super T10? They have a slightly lower 1st than a Muncie, and I thing they are evenly spaced all the way through.

Gary

Gary,

When GM sold cars "back in the day" the choice of transmission was dictated by the engine size and rear axle ratio. Axle ratios of 3.73 and lower (numerically higher) came with close ratio transmissions (M21 & M22), while axle ratios of 3.55 and higher (numerically lower) used wide ratio transmissions (M20). The Transmission Ratios were as follows:

M20 Wide Ratio M21 &M22 Close Ratio

It's going to come down to personal preference, but if you plan on making 1 hour drives down the highway, believe me rear axle ratios lower (numerically higher) than 3.73 are going to drive you crazy. I have a 77 Z28 350 (modified) 15 inch wheels with a Borg Warner Super T-10 (M21) and a 3.73 rear. The Z28 has plenty of pick-up and the Tranny/Rear combo seems just right for street cruising and the occasional short highway trip. More than

Paul.

Hi and thanks for answering my post. Iwas looking into the super T10 but I was told by a trans shop that it wouldnt fit with my console and the shifter needed to be modified to work within the console. He did those fabrications and said it could get costly. How difficult could it be?

I spoke to a few guys who have close ratio muncies and 3.90s and they said its not bad and others told me to go with a 5 speed overdrive to get the best of both worlds. I may start looking into that but righn now I have to work with what I have. No matter what I end up with I'm still happy I have a piece of American muscle car history again. I always had regrets selling my other cars when I was younger.

Thanks again Gary

Paul...Thanks. Yeah I was told the same and others have been very helpful with their experience said that anything over the 3.90 will be screaming at 60 -65 and noisey as hell. I think that I will look for a good m20 that has the 10 slpine input like my M21 so I can swap them out and see which one I like better. The shifters and eveything else are the same so the swaps are easy. I want to drive the car enough to enjoy it not look at it in my garage and never take it out. Besided there isnt much going on on the streets as far as street racing from light to light anymore. Maybe an an occasional rice burner import wit a big muffler trying to act cool. As long as I can shred some rubber and have it stick to his winshield as I blow by him, that wouls keep me happy. Thanks Gary

The only difference between the wide and close Muncie is the main drive and cluster gears. That's where the ratios are different. The M21 uses different gears, but there is no wide version that I know of.

Al

I would think that with the big block and all that torque 3.73's would be a good choice if you drive it on the highway. It also depends on how tall your tires are and what you plan on doing with the car... Remember 4th gear is 1 to 1 so just calculate what RPM you would be running with the different gear combo's and go with what you want to turn at 60...

Wish I could help more, but I had 5.43 gears in my '72 Camaro RS with a

Hi Gary, I have a 70 Camaro with the wide ratio in it, 3.55 gears and

I used to own a car with an M21, and first was a bit tall for good launching (that car had 3.31 rear gears), but the split from 1st to second was much nicer. By comparison, I actually like the 3-4 split in the M20 better than the M21. The M21's spread for 3-4 seemed a bit too close.

Frankly, I know the new aftermarket 5 speeds are expensive, but knowing what I know now, my advice would be to avoid spending big money on an old 4-speed, and save for a 5-gear. Keisler Engineering ( they are in the new Car Craft) has shifter kits for most old iron which makes an install mostly painless. I once drove a later Firebird with a 5-speed... ah, it was so relaxing. Anyway, the 5-speed is what I'm shooting for, since my old 4-speed is starting to show its age. Hope this helps. Good luck.

Ken

Interesting. The one/two split in a wide and close Muncie are exactly the same. The ONLY difference is third to forth. If you look at a parts list the only difference is the main drive (input shaft) and cluster gear.

For a close ratio box I would not go lower than a 3.73 gear. Chevy sold lots of cars with close boxes and 3.31's, not a good choice for a street rod. I had a Pontiac with 3.42 gears and a close box. It must have weighed 4,000 pounds. It was decent from a roll but slow out of the gate.

Al

Actually, the ratios are different. The M20 features a steeper first AND second gear, but the split between them is larger. It isn't a huge difference, but multiply it by 3-4 thousand rpms, and it becomes noticeable. Here is just one website which gives ratios for the different Muncies:

Also, bear in mind that a large number of the M20s were Saginaws. I don't remember now, but second in a Saginaw may have been taller than that in a Muncie.

Ken