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
Last edited by AutoGear; 03-12-2012 at 08:40 AM.