[importsmasher]

I have a 73 Ventura Sprint (74 GTO clone) with a 455, stock 6x-8 heads, Comp "280" cam (230° duration at .050, .480 lift), Holley 750 on a stock intake, and long branch manifolds with 2.5" exhaust. It has a 4-speed and a 3.73 10 bolt. It runs 13 flat at 105 on street tires. I have broken two axle shafts on the 10 bolt, so I used part of my tax return and ordered a Moser 12-bolt (3.42 gears, True-trac posi, 33 spline axles). I plan to get some stickier tires, which leads me to my next weak link - the Muncie. It has held up admirably over the last 10 years of abuse, but that was with street tires (best 60-foot time of 1.87). Eventually I want a TKO, but for now I am thinking I might upgrade the Muncie to an aftermarket case, steel midplate and M22 gears. I already have an M22 input shaft, and 2nd and 3rd gears, and I can get the rest of the parts for around $700. Any thoughts on how much abuse this will take? Anyone else running a Muncie reliably?

I will be out abusing my new differential at the Pontiac Heaven event on April 5....

Thanks, Importsmasher

[baron_]

i'll go out on a limb and do some guessing...I don't own an automatic car
+/- 50 horsepower


400 - 450 horsepower = M20
450 - 475 HP = M21
500 or so horsepower = M22

I agree with the typical statement that it depends on the muncie. In particular, make sure the linkage is adjusted well

that autogear conversion supposedly pushes it up to 600 horsepower

[Colin]

I would sell it and save up some more money and go with something else, maybe a TKO 600 or a Jerico. You can get a Jerico DR-4 with road race sliders for under $2600 (last time I looked, about a year ago) and I doubt you would break that.

[Colin]

OK, I just checked and the Jerico is a little higher now......
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Drag Racing 4-Speed, Clutch-Type, Top- and Bottom-Loader (#DR4)
Caged needle bearings are now standard in the cluster. Jerico® is always improving. New alloys and evolutionary gear design changes continuously increases strength and decreases power loss. $2,750.00
Optional road race sliders are free....they will allow easier downshifts.
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I would imagine you would have a hard time breaking a Jerico.............personally, I would buy that before I would waste time and money to modify that Muncie. Just my opinion........

[Bob with the 66]

Importsmasher,

I just went down the same road last year. 570 HP/ 590 TQ at the engine, new Centerforce DF, new 12 bolt, 35 sline strange axles, Detroit locker, new driveshaft with 1350 u-joints, and new rear suspension. My weak link was my original M-20.

I left third gear on the road one sunday night taking my wife for a ride. I have since replaced it with a Auto Gear M-22 Super case combo. I have had no problems yet, but this year the car will have a set of new M/T slicks. I'm keeping my fingers crossed.

Don't find the weak point the hard way, keep upgrading.

Best of luck, sounds like a very cool ride.

[ponjohn]

It is not the HP that kills them it 550+tqe that will destroy them with traction.

If you can manage the tque properly they will prob live. If you look up Guidos on this site he went to a dual disc adj friction clutch which comes in "soft" then grips. NOT cheap.

TKO is good but not bulletproof either, if you're serious about running a clutch car investigate a Jerico---again not cheap.

I hope you're already running a block plate and scatter shield??

[importsmasher]

Thanks for the replies. Unfortunately, buying the 12 bolt to fix my first weak link sapped all my money, so a Jerico or TKO is not an option right now and I am not willing to run an automatic.

I will refrain from running too sticky of tires, and will (hopefully) soon upgrade my M20 to an M22 as I mentioned ($700 instead of $2700), and hope for the best....The M20 has held up so far, as I have been running this combination since 1998.

Ponjohn, I do have a scatter shield, Hays flywheel and CenterForce clutch.

Importsmasher

[Cammer-6]

Just curious but has anyone found those Muncie replacement gears,parts etc that are American made?
All I ve found is India,Spain,Pakistan and of course China.

[ANDYA]

The gear sets that come in the supercase muncie are supposed to be made in Italy by a company that supplies the auto industry with OEM gearsets.
Importsmasher, if your going with 3.42 gears then I would go with the m22w gearset from Autogear in your muncie. The gears are cut straight like an m22 for strength but are a wide ratio like your m20. Close ratio gearsets are better with rear end ratios 3.90 and up and wide ratio 3.73 and down as a general rule.

[importsmasher]

ANDYA,
I will be going with the close ratio gears simply because that is what I have. I got the input, and 2nd and 3rd gears for free (new in the box), so I will be purchasing the compatible cluster. If I was buying everything from scratch, I would go with the wide ratio gears. For the rear end, I really wanted to go with a 3.23 ratio, but Moser doesn't offer it (the 10-bolt I am replacing is a 3.70). I know the factory used close ratio on 3.90 and up, but none of my cars seem to care. I have a close ratio in my 67 full size wagon with 3.23 gears (only because the $50 transmission I found was a close ratio), and I tow with it regularly. Also, I had close ratio gears in my 66 GTO convertible (3.55 rear), and when I had the transmission out recently, I put the correct wide ratio gearset in it, but I can't tell the difference. I don't remember if the transmission currently in my 74 GTO is close or wide ratio.
Importsmasher

[Prodart440]

Hey Importsmasher. If you aren't careful on what you build, your brothers 'cuda might be faster!!! HAHAHA!!

Aaron