Thread: 427 & muncie 4speed

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hello

i have a muncie m20 4 speed i will be running
a 427 with 450 horse the rear end is a 12 bolt
with 373 gears my question is will the muncie
be able to handle the 427 ? this is in a 57 2dr hdt.
chevy
thanks

I thinkthat depend on your driving. are you racing or just showing off on the street? What kind of clutch? Center force makes some really nice performance clutches as well as Ram. I see no reason why that mucie wont do the trick. Remeber no matter what you get and how much you spend. it can always break.

You need a M22, there are 7 different Muncie input shafts. All 26 spline inputs came with 32 spline output shafts and all 10 spline inputs came with 27 spline output shafts. A common mistake is thinking that all "fine spline" 26 spline input shafts are M22 heavy duty types. This is not true. An M22 gearbox has a 20 degree helix angle on the gearset as opposed to a 45 degree angle. Also M22 gear sets were of a higher nickel alloy. The straighter angle was designed to produce less end loading of the gear train and less heat but created more noise, thus the nickname "rockcrusher". The higher nickel alloy allowed for more impact of the gears. Another misconception is if you have a drain plug you have an M22. Again this was only true when the first M22 boxes were created. But all 3925661 castings had drain plugs.

If you can't get your hands on an m22, converting an m21 is a possibility. The cases are identical and I think the shafts may also be, so you just need the gear sets.

MUNCIE TRANS INDENTIFICATION
Case casting numbers, relating production years and ratios available
Casting: 3831704 Years: 1963 Only Ratios: M20 2.56 1st , M21 2.20 1st
Casting: 3851325 Years: 1964 - 1965 Ratios: M20 2.56 1st , M21 2.20 1st
Casting: 3885010 Years: 1965 - 1967 Ratios: M20 2.52 1st , M21 2.20 1st, M22 2.20 1st
Casting: 3925660 Years: 1968 - 1970 Ratios: M20 2.52 1st , M21 2.20 1st, M22 2.20 1st
Casting: 3925661 Years: 1970 - 1974 Ratios: M20 2.52 1st , M21 2.20 1st, M22 2.20 1st
Ratios of the M20 , M21 , M22
Year 1963-1965 Type: M20 Rings: None Ratio: 2.56 / 1.91 / 1.48 / 1.00 / 3.16
Year 1966-1974 Type: M20 Rings: Two Ratio: 2.52 / 1.88 / 1.46 / 1.00 / 3.11
Year 1963-1974 Type: M21 Rings: One Ratio: 2.20 / 1.64 / 1.28 / 1.00 / 2.27
Year 1967-1974 Type: M22 Rings: None Ratio: 2.20 / 1.64 / 1.28 / 1.00 / 2.27
Input Shaft Tooth and Spline Count Related to Year
Year 1963-1965 Type: M20 Rings: None Spline: 10 Tooth Count: 24
Year 1966-1970 Type: M20 Rings: Two Spline: 10 Tooth Count: 21
Year 1970-1974 Type: M20 Rings: Two Spline: 26 Tooth Count: 21
Year 1963-1970 Type: M21 Rings: One Spline: 10 Tooth Count: 26
Year 1970-1974 Type: M21 Rings: One Spline: 26 Tooth Count: 26
Year 1967-1970 Type: M22 Rings: None Spline: 10 Tooth Count: 26
Year 1969-1974 Type: M22 Rings: None Spline: 26 Tooth Count: 26
Reading Serial and VIN Numbers
Serial numbers for Muncie 4 speeds always begin with the letter "P". P stands for Muncie. Why.... I have no idea. The serial number is a date code the transmission was built for a particular year. Serial numbers from 1963 to 1966 included only the month and day. P0101 would indicate January 1st. From 1967 to 1968 the serial number got a year designator and a letter designator for the month such as P8A01, meaning January 1st 1968. One important point is that if you have a Muncie dated with a December build date it was actually built the prior year. An example would be the date code P8T13. This is for a 1968 production car. The T stands for December and 13 is the day. To confirm this simply look at the VIN number. It will usually begin with a 18S101350 or a 28N12950. This means the Muncie was assembled December 13, 1967 for the 1968 model year. The VIN number will usually be a low number. 1969 to 1974 Muncies got a ratio designator at the end of the serial number. An example would be P4D23B. This equates to April 23, 1974, M21 ratio.
Month Code Chart
January Letter: A May Letter: E September Letter: P
February Letter: B June Letter: H October Letter: R
March Letter: C July Letter: K November Letter: S
April Letter: D August Letter: M December Letter: T
Ratio Code Chart
Letter: A M20 Ratio
Letter: B M21 Ratio
Letter: C M22 Ratio

Re M21, there were also two different counter shaft sizes. The early ones were 7/8", later ones were 1". Early cases could be bored out for the larger shaft, a not uncommon modification. As indicated, if you don't beat on them too hard they will hold up, but the M22 would be better.

Thanks Bob, that was one I didn't know

I can't speak to specfics, only experience. I had a 1968 Biscayne, 427/425(NHRA rated 440 hp) with 4 speed and 4.10 12 bolt. It had a wide ratio 4 speed which according to the list Viking posted would make it an M-20. The car weighed 4080 with me in it and a full tank of gas. That 4 speed stood up to 4500 RPM launches with slicks at the track and 6500 RPM power shifts. It was also my daily driver. The only drive train failure I had in 2 years was a clutch that burned up when I tried a series of 4000-4500 rpm launches with slicks on concrete. I am guessing your '57 is lighter than my Biscayne so you can take my experience for what it's worth.

Pat

P.S. Darn I wish I had that car back!

Here ya go Pat, even though it's a '67 it should give you a little fix. BTW, I've got a Super T-10 that holds up to the 468 just fine.

Thanks for the "fix" Bob. I had admired your car in the Gallery before, she's a beaut! or should that be Brute? I bet most folks don't even realize what you have there.

I have occasionally thought of putting together a clone of my old car, 65-68 Biscaynes and Bel Airs are still pretty available. Much cheaper to do than a Chevelle, Nova or Camaro. There are still some originals running around, but folks seem to be pretty proud of them $$ wise. Alas one car toy is as much as we can handle right now. Maybe if I sold the boat....hmmmm

Pat