[Slapz]

How much HP will a Muncie 4 speed hold. How do you distinguish between an M21 and an M22. The M22 is what they called the "rockcrusher" right? Is that the better trans. Want to put this behind a 648 hp blower motor, My gramma drives an auto, I just want to have fun!

[cobalt327]

Originally Posted by Slapz

How much HP will a Muncie 4 speed hold. How do you distinguish between an M21 and an M22. The M22 is what they called the "rockcrusher" right? Is that the better trans. Want to put this behind a 648 hp blower motor, My gramma drives an auto, I just want to have fun!

A stock Muncie- even the fabled 'Rockcrusher'- will not last long behind that much hp, at least not if there's any traction involved.

There ARE aftermarket parts available to make a Muncie strong enough to deal w/it, and there are other trannys altogether that might be a better choice like a Tremec 6-speed (RPM Performance, Finishline Transmission, The GearBox, D&D Performance have been mentioned on this board for Tremec 6-speed performance builds).

I'll leave it to AutoGear and any other members that may have more info for you on this.

Input shaft rings and other clues can help to determine a close ratio from a wide ratio from a 'crusher, but the best way to tell is to pull the side cover to see exactly what you have- gears can and often are changed during the life of a transmission, especially one as old as the Muncie. You can google "muncie identification" and get more info.

[Slapz]

Thanks for the info. I also have a TH400 (it's for sale on this site). I guess from what I hear that it can handle hp even in stock trim. I got a heck of a deal on this motor but it sounds like it's really going to cost me in the long run. A Tremec 6 speed would be nice, ya know anyone that has one laying around .....cheap? I also need to beef up the rear end. Looking for a ford 9 inch too. I've had this Muncie laying around for years and thought it would be fun (like back in the 60's).

[2old2fast]

For what muncie's are bringing & what you'll get for your 400 , you'll be better than 1/2 way to a tremec !!??
dave

[Mr. P-Body]

One of our friends/customers has a '65 GTO he drag races. In the earlier days, he used the Muncie. By the time power levels got beyond 500 HP and 500 lb. ft., the "little" Muncies (M-20 & 21) were proving to be not up to it. Tried an M-22 (large output shaft, TH-400 "yoke") for a while. They too, cracked the cases. Liberty gears and a steel mid-plate helped, but never got a whole season out of it. He runs a Jerico now. But this is a fairly heavy car with a high-torque Pontiac in it. It 60'-s in the 1.4s and goes 10.30s right around 130 consisitently. That's asking a LOT from a "stock" transmission.

Many of the T/A crowd use the Tremacs. The Kiesler "kits" are very popular. For a "drag" application, not the better choice. For a FUN street car, the 900 should take the power.

Another 4-speed option that can take as much as the Muncies is the Borg Warner ST-10. I like the older iron-case version better for drags. But a good, tough trans.

NOTE: My knowledge and experience with the Muncies and the "partculars" is strictly from the '70s and early '80s when they were still plentiful in cars. I can't "swear" to all the correct designations, just what we were calling them "back in the day". Best recollection follows:

Earlier versions were around, but rare. These are the "popular" ones beginning around '63 (I think)... I've seen a few from Bonnys and Catalinas with the "long tail". Odd-looking...

M-20 "wide ratio", usually behind bigger engines in heavier cars with "normal" gearing 2.56:1 1st (?)

M-21 "close ratio", usually in cars with high-powered engines and "stiffer" gearing. 2.20:1 1st

M-22 came in both configurations ("close" and "wide" ratios), upgraded gear quality and larger output shaft. Later muscle cars.

M-37 "Super Muncie" or "rock crusher" Several ratios available, large input shaft (1 1/4, like "Hemi" 4-speed and "big" Top Loader), spur-cut 1st gear (increased load "shock" capability, makes a horrid "whine", thus the nickname) and large output shaft. The only cars I recall them in were the ZL-1s. LOTS sold over the counter for racing in the '60s. If someone reading this has more specific detail on this one, I'd really like to know more.

Most of my Muncie work was in Pontiacs. Some of the designations, gear ratios, etc. are different with the Chevy versions, but for the most part, they're "the same", as are the Buick and Olds. I recall Pontiacs have the speedo drive on the left and at least some Chevys, they're on the right.

There's an Italian-made version of the M-22 available "new" today. They call it "Super Muncie". Reports are favorable, but I have no "hands on" with it. A search would turn up a vendor.

For a "road car", I prefer the "fine" spline. 26, I think. For a drag car, the "course" (11) has greater "shear" strength.

FWIW

Jim

[Slapz]

Thanks for the input. This motor kinda fell in my lap, looks like it could be fun, BUT I'm on Uncle Sams dime and not a lot of extra coin. Trying to use what I have until whatever weak link breaks, then fix as you go. It would be nice to build a car 100% right out of the box but time and funds are a restricting factor. Just getting that monster running in my garage IN THE CAR gives me wood thinking about it. This has never been together before. I don't know if I've posted this but I picked up a '41 Chevy car frame that has a mustng IFS in it already and the frame is square. The stock truck frame is a "C" channel would have needed something (IFS, clip, whatever and the frame boxed). This saved a lot of work and I'm going to cage it and add reinforcenment. Needs all new wiring, and interior, and, and, and, MONEY. I can only go from there. A 4 link, roll cage, Tremec, ford 9 inch are like sugar plums dancing in my head.

[cobalt327]

Originally Posted by Slapz

Thanks for the input. This motor kinda fell in my lap, looks like it could be fun, BUT I'm on Uncle Sams dime and not a lot of extra coin. Trying to use what I have until whatever weak link breaks, then fix as you go. It would be nice to build a car 100% right out of the box but time and funds are a restricting factor. Just getting that monster running in my garage IN THE CAR gives me wood thinking about it. This has never been together before. I don't know if I've posted this but I picked up a '41 Chevy car frame that has a mustng IFS in it already and the frame is square. The stock truck frame is a "C" channel would have needed something (IFS, clip, whatever and the frame boxed). This saved a lot of work and I'm going to cage it and add reinforcenment. Needs all new wiring, and interior, and, and, and, MONEY. I can only go from there. A 4 link, roll cage, Tremec, ford 9 inch are like sugar plums dancing in my head.

Until AutoGear gets the chance to fill you in on the ins and outs of a beefed Muncie and info on them, etc. let me just say that the Muncie will last. Until it hooks good, that is.

The point is, you can certainly use a stock Muncie M20/21/22 to get the vehicle up and running. While the straighter cut gears of the close ratio M22 are stronger than the wide ratio M20 or the close ratio M21, w/a blower motor you don't need a close ratio box to keep the engine in the power band- you'll have a wide-as-the-Mississippi powerband as it is, and to use a close ratio box necessitates a lower (higher numerically) rear gear so there's not excessive clutch slippage in first to get underway. The lower rear gear ratio also means a faster driveshaft RPM and more engine RPM at any given cruise speed on the highway, and that gets old fast.

That leaves you needing an aftermarket wide ratio gear set and the other goodies that are available to beef up the Muncie, or an OD manual. It's up to you to determine which way to go, but like I said, for now you can use the stock box if you take it real easy on it.

As for the TH400, it can be made to handle a lot of HP, so can the TH350 and Powerglide for that matter. But if you have your heart set on a manual...

[Slapz]

Thanks for taking the time to repond to my inquery. I have a long way to go on this as none of this stuff has ever been together. Thinking about a front motor plate to secure this motor and add some rigidity to frame. I have pics of other frames and the way guys have strengthened them. I'm new to street rod building but have built a few ground up Harley choppers (wanna buy one?). I could get some good stuff with that money. LOL I have a couple of projects blocking my garage that I have to get out of the way. I'm sure you haven't heard the last of me yet. I should post some pics as maybe I'll get more helpful input from you guys.

[AutoGear]

For your application; M22W 2.56 1st gear, italian gearset with 3.55s or higher (numerically) gears in the rear.

We're the folks that designed the Italian gear program with Antonio Masiero (now Euroricambi). There is no way Id ever attempt what you're doing with anything less than an italian gearset. Today there are ways to get over 20 ratios between our M22 and Dragrace M23 programs. For you; I'd recommend a couple things. Firstly, I would get a SuperCase and an Iron Midplate. These 2 things will add a tremendous amount of strength to the equation. I would not re-use a gearset from the factory case. Factory cases are known to stretch over time and slowly pull the mainshaft gears and countershaft gears out of parallel. This means the gears are 'worn' into each other and will not play nice with new gears or a new case. This leads to a lot of noise and a short lifespan. I would insist on a 26 spline input, hopefully with an oilseal and you could go 27 splines on the mainshaft if its a street car, but Id prefer to see you with 32 splines on the output.

In order to tell the difference between an M21 and M22 definitively is to look at the HELIX ANGLE on the gearset M21 and M20s have a steeper pitch, where the M22 will have a less aggressive pitch. M22s are NOT straight-cut or 'Spur gears'.

We have never called our complete transmission a 'Super Muncie' in fact, we don't even use the term 'Muncie' to refer to our complete gearbox unless its a 'Muncie Replacement.' As the producer of the product, we're very mindful of stepping on GM's toes and infringing on their name, although we do make replacement parts for GM's muncie

There is no sense in using an M21; there are no premium quality gears, and by changing the input and cluster, you get an M20 which has a deeper 1st gear and is better suited to street cars these days.

Leave the numbers matching stuff to the restoration guys; its cheaper that way. A SuperCase retails for less than 300 bucks and an iron midplate is less than $100. Most shops charge 250 just to repair a used case.

With Respect to the M20 M21 and M22; these are technically GM 'RPO' production codes. If you wanted a wide ratio 4speed it was RPO 'M20' However this code also meant Wide ratio Saginaw 4speeds and T10s depending on the application and year.

Additionally; M22's are NOT 26 spline inputs and 32 spline outputs. This is YEAR specific (1970) not MODEL specific. There are probably more 26 spline input, 32 spline output M20s in the world than any other Muncie.

The GM Muncie is stronger than the T10 or ST10. The reason GM went to the T10 after the muncie was dropped in 1974 is that the T10 is less expensive to produce and the horsepower levels had dropped significantly by then. Some guys do impressive things with the T10; however, Richmond Gear was bought out and at the present time, the availability of T10 parts is getting scarce.

If you want me to locate a shop in your area that handles Auto Gear 4 speed parts just ask. One of our approved vendors should be able to help you out for about $21-2400 depending on options

[cobalt327]

I've posted this a few times; one more can't hurt. As said, the M22 has straight-er cut gears, not straight cut gears. No telling how many times someone has passed up a M22 because the gears weren't straight cut...

[Slapz]

Thanks for the comments and info. Haven't had much time to work on project lately with spring yard work and all. May just "go for it" with what I've collected over the years while I'm still young enough to do it (65). Buncha work that has to happen to get this running as is. As I've said, never done a ground up on a car so have a learning curve. Too bad there wasn't somebody in the area (Oswego, IL) looking for a garage buddy to hang out with so I could pick his(her) brain. Later

[cobalt327]

Originally Posted by Slapz

Thanks for the comments and info. Haven't had much time to work on project lately with spring yard work and all. May just "go for it" with what I've collected over the years while I'm still young enough to do it (65). Buncha work that has to happen to get this running as is. As I've said, never done a ground up on a car so have a learning curve. Too bad there wasn't somebody in the area (Oswego, IL) looking for a garage buddy to hang out with so I could pick his(her) brain. Later

Ha! I heard that. I could get a LOT more done around here if I only had a 20-year-old to mentor (read work his a-- off) in exchange for teaching him some tricks of the trade.

[2old2fast]

Slapz, I'm in ottawa [about 45 min] P.M. me , maybe I can help.

dave