How much (or little) can this rear-end handle.

I'm trying to decide what crate engine to get when the heads die on my 305 - I'm torn between a 350 (and what 350) and the ZZ383. I like more power, but I also am not rich.

So, if this thing has to be pulled for either motor (figure for 350 - max would be ZZ4), then what rear end should I get.

If I'm safe with this rearend for a ZZ4, then I think some 3.73s will be in order shortly.

Thanks.

 

do a search for "Magilla"

This guy had a 455 Buick in his 87 Trans Am and ran 11's. He used his stock rear end with the later 28 spline axle shafts and genuine GM gears. He said he broke aftermarket gears...

Every once in a while he would bust an axle shaft. Now you can buy super upgrades from summit racing for 230 bucks a set, complete.

If you can find a Dana 44 from a turbo T/A or a Firehawk you'd also be good to go. Our stock rear ends are not too tough.

Just food for thought.

 

How about a 10-bolt from a 4th Gen F-body? How much power can those things handle?

 

It's the same thing just slightly wider.

The 7.5/7.625 10 bolt has been broken on the street by a V6 and has survived 11 second passes on the dragstrip with a BBC. There's only so much you can do to beef it up but the tiny ring and pinion will always be the weak link.

 

Hmm, oh, okay. Then why would anyone want to swap it into the car?

So, I guess I'll have to go to a junkyard and look for...something?

I mean, I can't imagine there being a ton of Turbo T/As in the junkyard, or on ebay...

Nothing else will work?

 

The only diff that's a direct bolt in to a third gen is from another third gen or a fourth gen. Nothing else in the junkyard will work without a lot of modifications.

The 7.5" 10 bolt is the weakest. If you're lucky, you might find a 7.75" 9 bolt which is much stronger than the 10 bolt but aftermarket parts are non existent or extremely high priced. Finding the very rare Dana 44 would be an ultimate find. They came in the SLP Firehawk but were also available over the counter from GM many years ago so someone could have installed one into any third gen. The Dana 44 is a 8.5" ring gear and the best factory available diff for the third gen. The Dana 44 is common as a front differential in 4x4 so there's lots of performance parts available.

The only other option is to buy an aftermarket, direct bolt in, 9" or 12 bolt. Expect to pay $2500-$3000 for a complete, ready to bolt in, diff.

Looking under a third gen at the diff cover. 10 bolts and a smooth cover is a 7.5" 10 bolt. 9 bolts and a rubber plug in the cover is the Borg Warner 9 bolt. 10 bolts with a metal plug in the cover is the Dana 44.

The best suggestion is run what you currently have. If you ever break the differential, then decide how much it's worth to upgrade. The 10 bolt is stronger than most people give it credit for. Trying to upgrade or modifying the 10 bolt to be stronger can cost more than just buying a 9" or 12 bolt.

 

My stock 86 7.625 10bolt is still rockin with the 355 and 420+HP/TQ. Its not as weal as most will think. Slicks and drag racing isnt going to be good on it though. Mine isnt abused like that. But 21 years, new bearings/races/Auburn LS/3.42 gears and daily drives with some track times on radials it has been very loyal. Aftermarket gears whine a little. But Ive never thought it would let go.