8 3/4" How Strong?

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Murray

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My first time with big power. '68 Dart, 606hp sbm, Tremec, Gerst suspension. Want to run autocross, but streetable. Do you think an 8 3/4" is a good choice? Will it handle 600+ hp? Maybe a "built" 8 3/4"? What do you think? Thanks.
 
The 8.75 is capable, but by the time you build it stout enough, you'll have enough money invested to more than cover something like this fabbed (and much stronger) 8.75 housing from Moser:
8 3/4 Mopar Fabricated Housing & Axle Package - Moser Engineering
And you still retain the easy carrier/gear interchangeability of the 8.75.
Or just build a Dana 60 if that doesn't matter to you.
 
I would think autocross would not tax the strength of any rear end.

Now the rigidity of the rear and the rear suspension is another thing.
 
I think that if a dana has a gear ratio you can live with, i would go that route, rather than put a bunch of money into an 8 3/4. I realize you are talking street use and autocross rather than high traction/high stress drag racing app, but I still don't care for 600hp/manual trans/ 8 3/4 combination.
Then there is always the heretic option.... a nine inch. Much better ratio selection, replaceable center section, lots and lots of strength upgrades available, and can be built much stronger than a 8 3/4 (my opinion).
 
Agree with Rusty

If you like the idea (I do) of being able to swap gears fairly quickly, I would go Ford 9" PERIOD

If you are pretty sure of what gear you want and fairly sure you won't have to pull it apart, then there are a "few more" options. The "usual" of course is a Dana. Expensive to modify and get together, but you most likely will not hurt it.
 
I think that if a dana has a gear ratio you can live with, i would go that route, rather than put a bunch of money into an 8 3/4. I realize you are talking street use and autocross rather than high traction/high stress drag racing app, but I still don't care for 600hp/manual trans/ 8 3/4 combination.
Then there is always the heretic option.... a nine inch. Much better ratio selection, replaceable center section, lots and lots of strength upgrades available, and can be built much stronger than a 8 3/4 (my opinion).
I've never seen it as the "heritic" although I know what you're sayin. Too many chest thumpers think "Mopar or nuthin" and in some cases they are just plain wrong.

I've always thought the 9" was in the same favor as the early Hemis. They will go good in anything. Looking back at hot rod history, the rear end of choice was the Oldsmobile third member style, before the 9". They were under everything from street cars to early fuel rails.

The 9" has SO many available ratios and upgrades and the parts availability is simply off the scale. They are stupid strong even in stock form. If you use one and have a drive line failure, it probably AIN'T gonna be the rear end.

And of course there's that cool bench racin thing when somebody asks you "Hey Rob, what rear end you got under that?" Somehow when you say "9 inch" it just sounds cooler. lol
 
I've never seen it as the "heritic" although I know what you're sayin. Too many chest thumpers think "Mopar or nuthin" and in some cases they are just plain wrong.

I've always thought the 9" was in the same favor as the early Hemis. They will go good in anything. Looking back at hot rod history, the rear end of choice was the Oldsmobile third member style, before the 9". They were under everything from street cars to early fuel rails.

The 9" has SO many available ratios and upgrades and the parts availability is simply off the scale. They are stupid strong even in stock form. If you use one and have a drive line failure, it probably AIN'T gonna be the rear end.

And of course there's that cool bench racin thing when somebody asks you "Hey Rob, what rear end you got under that?" Somehow when you say "9 inch" it just sounds cooler. lol
Mopar is my favorite brand, but I like to think I'm open minded about rear ends. I currently have a Dana suregrip, an 8 3/4 locker, a nine with a spool, and a nine with a locker in use.
When (if) I get the stroker in my 62, I will sell the nice 8 3/4/locker to finance a Dana.
Edit: and yep, the pumpkin style Olds and Pontiac were hugely popular in the sixties, many times stronger than the early ten bolt Chevy, and a direct bolt-in in a shoebox.
 
If you are hooking on launch with that much power you will break things.Street tires will
just break loose.Slicks and suspension for them are a different matter.
 
My first time with big power. '68 Dart, 606hp sbm, Tremec, Gerst suspension. Want to run autocross, but streetable. Do you think an 8 3/4" is a good choice? Will it handle 600+ hp? Maybe a "built" 8 3/4"? What do you think? Thanks.
It’s more of the amount of torque vs weight and the “Hook” of the vehicle and of course, the amount of abuse. This is a very blurry line to have anyone make a call on. It seems that around the 600+ ft. Lbs. of torque and a 3600 lbs car, the ghost is given up after a short time. Sometimes more, sometimes less. Dropping the car weight would help a lot in longevity as well as beefing up the rear.

I would not bother beefing up the rear beyond high strength axles and braces across the back side and the spring perches. These are cheap and easy DIY jobs with a welder. Of course the 3rd member is upgraded with a new carrier and gears to suite the task at hand, but that’s the case with me on any gear change I do with this rear. I don’t consider this part of the price upgrade tag but just par for the course since the OE stuff, I tend to break.

Go to doctor Diff and have a poke around.
 
Might want to think about a Panhard bar. The T/A - AAR and darts used for road race are all set with them. Also 9/16 or larger wheel studs. They also add floor supports to tie the frame rails together with the cage, subframe connectors, torque box’s and other tricks. With that much power, your just asking to twist the beer can….
 
The stronger the rear axle, the more its going to weight. The more weight, the more poorly its going to handle. For autocross it would be best to back off max torque and horsepower and build a engine with good torque matching the rpm it comes out of corners at so it pulls hard and match the lightest rear axle that will handle that power.
 
The stronger the rear axle, the more its going to weight. The more weight, the more poorly its going to handle. For autocross it would be best to back off max torque and horsepower and build a engine with good torque matching the rpm it comes out of corners at so it pulls hard and match the lightest rear axle that will handle that power.
I tell you what comes to my mind when you said it like that. A beefed up 8 1/4.
 
I tell you what comes to my mind when you said it like that. A beefed up 8 1/4.
I agree, or an 8 3/4 with aluminum center section, beefed up housing, caps and axle. All the same issues with an 8 1/4.

really, what is the tipping point from handling to horsepower/ torque in autocross?
 
I agree, or an 8 3/4 with aluminum center section, beefed up housing, caps and axle. All the same issues with an 8 1/4.

really, what is the tipping point from handling to horsepower/ torque in autocross?
Heck if I know, but honestly, a 9" ain't gonna lose him any races. It's really splittin hairs. Now, a Rockwell 2.5 ton axle is another thing. lol
 
The stronger the rear axle, the more its going to weight. The more weight, the more poorly its going to handle.
There is a certain amount of accuracy to this but the way you out it, it seems over stated. There is additional weight but not at a serious penalty. Drag racers can attest to this. Any additional weight can be wrote off as a reasonable penalty worth having in exchange of durability. The weight is unsprung.


For autocross it would be best to back off max torque and horsepower and build a engine with good torque matching the rpm it comes out of corners at so it pulls hard and match the lightest rear axle that will handle that power.
While an advantageous move, this is really hard to do from a new guy point of perspective. Changing conditions would have constant changing of equipment. Knowing the car and track as all as the engine power curves are where this all starts never mind the equipment being used. Just where this area of to much power is can not be determined by internet chatter.

Murry did say, first time with big power….
 
.....and if you have a typical front-heavy weight balance, a little rear-end weight won't hurt.
And since aluminum 8 3/4 centers haven't been made for about 20 (or is it more?) years, an aluminum nine center is probably about a quarter of the money of an 8 3/4.
 
.....and if you have a typical front-heavy weight balance, a little rear-end weight won't hurt.
And since aluminum 8 3/4 centers haven't been made for about 20 (or is it more?) years, an aluminum nine center is probably about a quarter of the money of an 8 3/4.
215 bucks from US Powertrain. Aluminum 9" case. Free shippin, even. lol
 
go with the 9 inch Ford , again as stated parts availability , strength ,gear ratios in increments of 10 to help tune your car for the track you are on ,,, the Dana has its place but gear ratio selection is very limited and gear changes can be time consuming . Nascar is an excellent example of what the 9 inch can handle 500 miles at more rpm than your car will ever see as well as the punishment on the road courses they run .. do it once and do it right ,, Moser , Strange etc. can build the complete 9 inch housing / axles and carrier you need ,, i suggest you go with 35 spline axles with a 35 spline Detroit Locker to keep the car street worthy.
 
If you’re not banging gears the 8-3/4 will last, it was used in 200 mph 4000 pound Daytona’s
 
DANA sounds better than, "I got a nine incher"...or you could call a Dana a "HEMI" rearend... I like Mopar parts in Mopars...kinda like how I like Ford Parts in Fordz....and Chevy parts in the backyard..
 
The Dana power lock sure grips seem to be a little bit stronger than the cone style... I seen a guy running 800 horsepower throw the tires in the air with a 741 case sure grip and got 20 passes out of it before he broke the Caps off... Which by the way is the failure point in 8 and 3/4 rear ends the Caps tend to snap but only if you're running lots of power. ... I've never seen it 8 and 3/4 pinion snap or fail ... Maybe the only exception to this is in the 489 cases without the crush sleeve delete. Remember even the 741 case has a larger pinion than a Ford 9 in in diameter .. my 416 340 running right around or just under 600 horse and I haven't broken any of my 741 cases yet. ( Not running a trans brake)
 
Teeth fail, snapped all off my 8-3/4 in 4 races. Dana went back in 93
 
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