Im looking to upgrade the standard diff in my 2wd sapphire cosworth which is 550hp before it breaks. Got the option to buy a full supra diff setup including fitting kit and billet rear cover. The diff has been checked over by a local transmission company and given a clean bill of health.
my question is, is it worth getting it rebuilt with the wier upgrade kit or not? Its pretty expensive to get done and wanted to see if anyone has tried them with and without the kit and can offer an opinion?
Im just a bit concerned if it will spin one wheel only when on the power as im not sure how well the standard supra diffs lock up to aid traction .

 

How much have you been quoted to fit the weir kit? Think mine was about 350

 

Bara quoted Ł545+vat and possibly + another 250 odd of it needs bearings.

 

Depends how you are going to get it to fit...off the shelf fitting kit or someone fabricating?

If you are going fabrication route I would look at some of the BMW diffs or Yank stuff as you can buy them in any ratio and you can get light weight alloy stuff that will take 700 bhp+ I have a Supra diff with weir kit but if doing it again I would go alloy as the Supra is a heavy bit of kit.

 

I'd be tempted to run as is only thing you have to lose is time in labour l, I'm sure thiers supra out thier on std rear diffs running more than what your running the crown wheel in these are beefy

 

At that power in a Cossie which is alot lighter than a supra and has skinnier tyres I would just run the stock diff if it was me

 

Supra diff is lsd anyway if from a turbo model so will lock both wheels

 

I’ll be using the mk fitting kit which im buying with the diff. Scooby, did your old supra just have the standard lsd? Did that spin both or just one wheel?

 

My supra had carbonetics diff and 295/30/19 r888s and a load of grunt lol
But that was a 3.4 with 800 hp and over 600 lbft of torque at the wheels, a yb at 550 hp id chance a standard one if it was me

Standard MK4 turbo diff be LSD 100%

 

295 or 305 r888s on low boost trying to grip, rods should be worse than that when I get it lol

Makes me want another supra listening to that soundtrack I better think of something else now, lovely weather today...........

 

Yea think il just try it as it is. How long till you get the sierra from mark? Guess you’ll have to wait a bit for better weather before you can use it much

 

I would mate will save a good bit of coin and a good chance it will be fine imo

The saphs just got final part throttle mapping left, abs to sort out and a new breather for motor and I can then pick it up

I wouldn't use it yet anyways so not to fussed atm, gtr is so close but again bad roads put a halt to finishing off setting up line lock and launch control today

 

Fitting a wier kit into a Supra diff is very simple iv fitted one in my focus Supra diff and modded a spare I have . If your not happy to fit it your self I would think the company that checked it over should be able to fit it as it does come with instructions on how to fit the kit .
i just went on the website checked out witch kit I won'ted and payed for a week or two later it was at my door

 

whats in the wier kit and where can you get them from Thanks

 

http://www.weirperformance.com/maxgriplsdkits.html

 

Quaife 7.5" 2wd diff in back of my escos 4x4 at over 600bhp, more than enough.

 

If your permanent 50 50 power split rear diff is only getting 300 hp to it though

 

60/40 and bags of torque and it hooks up not light Tyre's up

 

I’ve got three mates who have run gripper diffs and all three broke them at this power level, i think more than once too, i think one broke at 380 hp. Its broken all different bits too not just the cwp, broken the actual lsd unit aswell, hence not wanting to go that way with mine

 

Does anyone know out of interest which wier kit people tend to use as theres 3 options?

 

Imo your doing the right thing getting a supra diff they are just miles better to start with

 

It's kit 1. That's used in them mate

 

But thats only 360 hp to rear diff mate like a stage 3 saph and I never had any bother at stage 3 power with stock diffs

 

For that cost to add the weir kit I would just fit the whole kit as it is seeing as it’s all been given a check over and is fine as is.
You def won’t break it and they are still limited slip as standard so you’ll be fine 👍🏻

Cheers Paul

 

were you over 500 of torque at stg3, its not all about BHP matey

 

The Cosworth actually has a 34/66 torque split in the gearbox. So it is actually also 2/3 of 500 lbft going to the rear diff. Or did you already take that into account, that your engine has over 750 lbft?

 

i wish it did 🤣🤣

 

I think the torque split may be different if you have uprated viscous coupling...is that correct?

 

yeah thats correct and sequential, ya all just need to go 4x4 to give the rear a break 🙈🙈

 

I don't have torque figures to work with mate but I'd imagine a 600 hp yb will have torque below 600 anyways

My stg 3s I dunno what they made never had one dynoed, didn't have any boost control for big spikes of low down boost so I'd guess 350/350 maybe

 

I had a standard diff broke that at 350. Fitted a gripper and the guys told me your not brake that but you will brake the cwp. Had an m.a.d 500bhp set up and yep took all the teeth off the cwp coming off the roundabout in 2nd with r888’s. Absolutely no wheel spin it griped and went bang. Re built it with a hewland engineering shot peened and super finished cwp. Didn’t brake that. But it’s for sale now as I fitted a 6 degree rear beam and a supra diff with a weir kit

 

No it won't be different. The torque split is defined by the epicyclic gears in the transfer case of the gearbox. But the 34/66% torque split is only applicable when there is no wheel spin. If you want a different torque split you need different size gears in the epicyclic unit.

The viscous coupling determines how much torque is transferred to the front/rear wheels in case of wheels spinning, so in that case it is no longer 34/66%. An uprated viscous coupling will allow less wheel spin. It's basically the same as what a rear LSD would do.