Will this diff combo hold up to 350++ hp
 

Hey guys, I've done a fc subframe in my '83 S2 and I'm wanting to change the rear stud pattern.

I'm running (once it's running) a 13bT (TII) with a gt3582r that will be running upto 20+ psi.

The current diff is '84/85 S3 26 spline lsd unit (gsl-se) and I was about to order a pair of moser axles from Sam at re-speed to beef it up and do the 5stud change.

Am I dreaming that this will hold up??

The car is a street car and the 20psi will only get used occasionally. I'm hoping to do the odd circuit day in it, but I'm not into drags etc.... I'm getting too old lol
So what do we all think??

I want to avoid a Toyota hilux conversion if I can and a ford 9" (8.8) is a no no...

If the axles will hold up, what about the LSD centre?? I'm happy to change the centre to another unit like a guru or Kaaz if it makes the difference.

I should also mention another option i've got "if" i can find the suitable parts.

There was a Guru Torsen centre that takes 28 spline borg warner axles and there is a Aussie model Ford that has the borg warner axles that fit the S3 rx-7 housing.

However these centres are rear as hens teeth and i'm led to belive that they are no longer made new.

I'm guessing no one knows?

The S3 rear end will hold if its in good shape. The upgraded axles will make the
pumpkin (the center) the new "weak spot".

As long as you run "regular" street tires (so it will never "HOOK HARD") you will probably be
okay. Although at 350whp you're probably already at the limit of that rear.

If you drive like a human being, instead of John Force, or Rhys Millen, I think you'll be okay.
If it doesn't hold up, you can always upgrade later.

Good Luck

thanks for the reply.
Yeah i drive like a human. i'm not into drags etc... i will be running wide tyres, but in a road compound. The Haltech ECU can control the boost v/road speed or gear, so i can actually ease the power on in the tune/setup,but its still big HP regardless.

The LSD is in great condition too, however they are worth a small fortune over here, so i'd rather upgrade it before its busts.

Assuming i can't find the Guru 28 spline centre, and if the moser axles will hold.... I think iI'd look for the Guru Torsen in 26 spline, as these are a bit easier to find than the 28 spline one i've mentioned above.

what about the moser axles with a miata torsen? or am i dreaming? :-)

There's an OS Giken LSD for the Miata that will bolt in. Mikeric is running one with his 400rwhp-ish FB. That along with the axles should make it fairly well bulletproof for what your planning

Yes, but for the money he (Mikeric) spent, he could go with a cheaper/stronger Hilux unit.

how come you are avoiding the ford swaps? i mean, i personally don't want to swap in a ford rear end either, but my car will never see those types of numbers. If you are putting together such an awesome engine it seems like a great idea to me to upgrade to an axle with tons of potential to match, instead of hoping something inferior will hang on for awhile. The ford 9" has endless amounts of aftermarket support, gears, axles, lsds, brakes...but, just my thoughts.

Weight, and significantly increased drivetrain losses.

Anyone know how heavy the Hilux rear is compared to the stock one?

i want the same setup as mikeric..and send my stock gears to get headened...the 3.90 gear are the strongest ones out of gsl 84 85...my friend has a hilux in his 1st and i hate the way it handles....

Thanks guys, I don'd want the weight of a 9" rear. i'm into handling not drags and burnouts.

A hilux will work out better, but if billet axles and a new centre in the s3 housing i've got will do the job (properly) i'd rather go that way and keep the weight down.

The guru centres are tough as and are proven to 600hp, so if the mosler axles will hold up its only the r&p gears that will be the weak link from what i can tell.

the LSD centers are worth more over here than in the USA, so i can sell that to offset some of the cost of the guru centre...

So i guess a more specific question now is, has any one busted a mosler axle in a 1st gen?

well i hop i dont as i just placed the Order with Sam at RE-speed :-)

well..let us no how it turns out......good luck

First problem with your plan is this:

Unless you aspire to be nothing more than a trophy bottom, a 3582 at over 20psi should be quite a bit more healthy than 350whp. While you may have some life in the stuff at 350whp, it's borrowed time at 450whp.

The axles shouldn't give you any trouble. The diff will be iffy at that level, but there are differentials out there that will take it. I'm interested in the OS Giken simply because they make the finest diffs in the world.

I'd be worried about a couple things:
1: structural integrity. At this level the diff may start to flex and do funny things. The main caps may be suspect too.

2: the gear set: I shredded a 4.10 gearset at 250whp. I would recommend looking into WPC or heat treatment.

Ford 8.8
 

I'm in a similar situation -- over 300 RWHP and looking for more with a GSL-SE rear end. In my case, I have a lot already invested in it:
- Raised gear oil input port for increased oil capacity
- Full circumference oil dams welded into the inboard sides of the axle tubes
- New axle bearings
- Tri-link / Panhard conversion

Despite all that stuff, I think the best option for me if (when) I break something back there will be a Ford 8.8 rear end:
- Lighter and more efficent than a 9"
- More than strong enough
- Huge selection of diff and gear ratios to choose from
- Used on Mustangs, so they're plentiful and relatively cheap

Another interesting attraction for me is that the Mustang version comes with the attachment point for the upper 3rd member already built in.

The S3 housings are rather flexy. I remember someone (RICE RACING maybe?) saying that a S2 rear is stronger than the S3 rear, since while the S2 has thinner axles, the S3 housing flexes more, which puts more load on the axles. He was putting down something like 600hp so I'll defer to his experience.

I've twisted a couple S3 housings and the one in my car now has about an inch of toe-in... granted I'm not putting down 350whp, less than half that really :)

You'll find that 90% of gear breakage problems are really case flex problems. And in rearends that usually means the caps are shifting under load.

A Toyota 8" makes more sense. I'm personally probably going to find an Explorer 8.8 (not sure if these are available outside North America) because, even though it's heavy, they have beefy axle tubes, 5x4.5" bolt pattern, factory disk brakes (GOOD ones, with drum style parking brake), usually a clutch pack limited slip, 3.73 or 4.10 gears already in there, abut the right width, and they're CHEAP since C4C took a lot of them off the roads and into used parts inventory.