How much hp/torq will an OEM 833 4sp and 8 3/4 take?

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jimharvard

jimharvard

JimHarvard
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American Metal Direct (AMD) has finished converting my 69 M-Code Cuda from a drag car back to original factory construction. (see general discussion thread, "My M-Code is finally getting worked on.")

M-Codes were factory 383 torqflite Barracudas which were converted to 440's by the Hurst Corp and sold as "factory cars." mopar only put torqflites in the cars because they thought a 4 speed would either not hold up or would be abused enough to cause too many warranty claims. however, they did install the same 8 3/4 rear diff that all the Formula S and "Cuda package" cars came with.

the "standard" 440 that Plymouth put in the GTX in 1969 was rated at 375 horse and 490 lbs. of torq. but that car (and the A12) came with a Dana 60 rear end and the "Hemi" 4 speed. the A12 440 six pac motor was rated at 390 hp and 490 lbs. of torq.

i want to build the engine and drivetrain on my car the same as the A12 69 1/2 Roadrunner. however, a Dana 60 is a couple of inches wider than the 8 3/4 that came in 340, 383 and the 440 Barracudas. so i would like to use the 8 3/4.

so here's a couple of questions that i'm hoping someone in the FABO racing community will have some knowlege on..

1. will the "short" 833 4 speed that came in the A-Body Barracudas stand an A12 440?

2. will an 8 3/4 with a 3:91 posi stand an A12 440?

the idea of the car i'm building is to build "the M-Code that Plymouth should have built." the car will be a 440 six pac built to A12 specs with a 4 speed and a 3:91. i am not building this car to be a regular drag race car but i suspect i will race it a few times. i'm wanting to be able to smoke the tires at around 3500 in first gear and "power shift" second at about 6k.

what do you think ... will i "break" this car the first "vintage drags" i take it to?

thanks...
jim coster
pittsburgh, pa
 
Will be fine until you put sticky tires on it. Traction kills parts. I'm not sure what your build will consist of but sub 600hp should be fine. The rear will go before trans. Then clutch and the trans if you make enough power. A slipper clutch would cure this but more of a race setup. I'd talk to liberty
 
You can break a Dana if you hammer at it long enough. The 64 hemi cars did not come with a Dana I don't believe, nor an 18 spline
 
You would probably break a yoke before you kill an 8.75 or a clutch before the 833 goes
 
833's are pretty darn tough, It takes a good bit of power to kill a 8 3/4.But anything can be broken.I would say you will be just fine.
 
I agee don't dead hook it.
I looked into this because I have a large stroker motor in my Challenger with an 833 and 8-3/4.
The 833 is not the weak point, but a heavy car on the 8-3/4 would be the link.
You can beef it up and back brace it, but most would think at that point to buy a Dana and be done with it.
I've read on guys running said combo for years and no problem, and others who blew up the yoke or ring n gear right away.
 
If this is really a "what if" build I think you'll be fine.
The factory wouldn't tub the car so probably limited to A12 size wheels in '69.
Which I'm pretty sure were only 6" wide.
So, I'd stick with the stock wheel size, which should limit traction, and look more 1969!
And I'm not an A833 expert, but isn't there a 18 spline, "big yoke" version you could build?
I'm assuming this is what the '68 Hemi A cars used.
I believe most A 4 speeds used the small yoke.
Adding any external bracing to the rear would spoil the '69 look.
The factory would have probably run the Dana, not sure how wide the Hemi a cars were. Sounds like a neat build!
 
As long as the 833 is tight you should be fine.
Adding slicks you'll chase wheel studs, u-joints, and ring and pinion gear.
 
I like a roll control selenoid so you can load train up just enough to take out slack yet not slip clutch too much. Launch at 3800. Your 60' will suffer but you will make it to the end of the track. Maybe this is a given though. .02
 
From personal observations I can say an 8 3/4 will live behind an alcohol injected 450"+ Rodeck in a dragster on asphalt and on sand with paddle tires. I know, lighter weight. How many of us run an injected Rodeck on street tires though?
 
Clutches break parts. You can put a bunch more through a 4 speed and 8.75 than you are going to IF you get the right clutch.

IMHO, that would be a Sof-Lok from McLeod or similar. They are totally street able and won't break your parts.

They aren't cheap either. But neither is breaking parts.
 
thanks to all you guys for the great advice. i can always depend upon the FABO race comminuty to "know stuff."

"back in high school" (69-72) i street raced a (then new) 68 barracuda, formula S fastback, 340 4sp, 3:91. it was an all factory drive train with the 23 spine 833 and 8 3/4 A-body rear gear. the car came with original 14" x 6" "bias belted" tires but i did up-grade to "polyglass raised white letter" 14's that were close to 8" wide. a fastback 68 barracuda tips the scales at about 3200 lbs. and i never raced with more than me (175 lbs. at the time) and a similar sized passenger. never had anything in the trunk other than the spare tire. i beat this car every weekend doing 3500 burn outs in front of the Big Boy drive-in burger joint in my town and launched about the same in street races with power shifts at 6k. i never broke the trans or the 8 3/4.

the "M-Code Cuda" that i'm building with the A12 440 will be exactly the same car as my high school racer - except it will have the 440 rather than the 340. and since the extra weight of the big block is over the "front" wheels, my guess is that this car will just smoke the tires all the time and NOT break the drive line. i'm really just building a "really fun" street car and not looking at a competitive drag racer.

A-body's have about a 3" (don't quote me on that number) narrower rear track than B-body cars do so a Dana 60 has to be narrowed by about that much to make it work in an A-body. there was one of these narrored Dana's on ebay recently (and may still be there) that the guy was asking $1100.00 for. while the A12 Roadrunner used a 4:10 in its Dana 60, i can live with a 3:91 in an 8 3/4 now that you guys think that the rear chunk will hold up.

if i have more technical questions, i'll be back "bothering" you guys... thanks again... !!
 
I have heard of Dana's breaking & 8 3/4s. Also 833s 18 spline & 23 splines
 
Broke a yoke as mentioned, and shattered a 489 center but never the 833 trans.

I say build it, push it and let's find out!
 
Just don't put an A833 overdrive in it! The od gear is pretty weak. I took two of 'em out like nothing,with my 367.
And the CFII will destroy stuff if you start sidestepping it, at peak torque,lol.
I think YR is on the right track, in post #14.
Pick an R&P set with lotsa teeth on the pinion.The more the better.
 
say what you want so or later the 8 3/4 ring gear will go....as I go to garage this afternoon to swap out pumpkin ...that is going clunk..clunk..
 
70aarcuda said:
say what you want so or later the 8 3/4 ring gear will go....as I go to garage this afternoon to swap out pumpkin ...that is going clunk..clunk..
Click to expand...


I broke my 8 3/4 two times in my Demon. Ring gear once and the cap the second time. It was a stock interior full weight car with a 360 in it.
Demon 2 001.jpg
 
8 3/4 will break for sure. Mine was a full interior B-Body with near 5k launches and slicks. Smart driving will help. But seemingly this nice original 440 A-body that was turned from racer to resto at expense will not see this abuse!!!!!

Regain your senses Jim!
 
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light car, no slicks........you should be fine........
 
Deal is this a real 440 car! Put the auto back in and some convertor if you like but my guess is you are just dreaming! This car deserves it!!
 
He is just joshing!

You do not spend that coin to flip back the other way! This car will be much like mine that still has some umph and occasionally romped on, For the smile factor, It costs to much! 318 and slant cars are still plentifull for that abuse!
 
If Mr. Jim was serious then he would of had AMD install a 4 speed tunnel! LOL!
 
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