993PET

My '04 996 Cup Gearbox is being disassembled for rebuild. We discovered it has a
Quaife "Torque Biasing Limited Slip Differential" installed. I'm seeking opinions on whether I should keep it or go back to a factory or Guard conventional clutch type LSD. Anyone with experience of using the Quaife in a club race application good or bad please comment?

I understand it's not PCA GTC3 legal, I don't plan on running the car in GTC3 at the present time.

Thanks,

JF

coryf

Torque bias diff's go open under braking which makes it very unstable relative to a clutch/plate style. They also transfer all the power to the wheel with the most traction on corner exit which may be too much for one tire (instead of distributing the load between both). Also a standard non preloaded torque bias diff will act like an open diff and spin up the unloaded wheel if it comes off the ground like when hitting a curb. A conventional limited slip is normally much better in a 911. Torque bias diff's work well for front wheel drive or front engine rear drive cars.

993PET

Hi Cory:

Thanks for your reply, I'm a bit puzzled why anyone would put one of these in a Cup. Anyway this is the description from the Quaife website. I guess I'll be starting a WTB Fatory Cup LSD Thread!

"Quaife ATB Helical LSD differential for Porsche 996 G50 is suitable for Porsche 996 models with G50 gearbox. A direct replacement for the standard Porsche differential, the Quaife ATB Helical LSD differential transforms your car’s performance.
Unlike a conventional plate-style limited slip differential, the Porsche 996 G50 Quaife ATB Helical LSD differential relies on gears rather than clutch plates for its operation. That means it is much smoother in operation.
The Porsche 996 G50 Quaife ATB Helical LSD differential never locks harshly with a set pre-load of wheel slip across the driven axle, like a conventional LSD. Rather, the Porsche 996 G50 Quaife ATB Helical LSD differential automatically biases the torque away from the spinning wheel across the axle, to a constantly varying degree, and never locks.
The Porsche 996 G50 Quaife ATB Helical LSD differential has many benefits over a standard open differential, including maximising traction and minimizing wheelspin, eliminating torque steer and snatching in front wheel drive cars compared to conventional LSD units, and a maintenance-free design which retains the standard oil lubrication.
The Porsche 996 G50 Quaife ATB Helical LSD differential is proven in circuit and drag racing, rallying and road use, and is produced from Corus steel billets, and is CAD designed and CNC machined, then inspected to ISO 9001 standards."

bgiere

The phone call starts like this: Hello is this Matt Monson?...send me a Guard GT diff pronto!

jrgordonsenior

I had Matt rebuild my cup diff and it was a major improvement. Literally a second faster at my favorite track first session out. I'd price the OEM cup vs Matt's diff....

coryf

The low/no maintenance on a torsen is good but its not worth the negative affect on the handling. If you go with a factory diff, I would spend the extra money on the new style with the forged housing. The early (pre-09) have a cast housing that have been known to fail. The Guard diff is a great way to go, has a CNC billet housing and is a better price than the factory I believe. Also you would probably want to re-stack the plates in the factory forged diff since it is intended for the 997's which ran more pre-load and friction plates than the 996.

amso3

Don't even consider re-using the Quaife. Call Matt! You will not believe the difference in the breaking stability.

fstockcarrera

Cory, What is the down side of running the newer Billet Diff with more preload and plates in a 996 cup?

Thanks in adv Bob

GTgears

Cory,
We do NOT make forged anything!!!! All CNC billet. A VERY important distinction. Forging a are only as good as the materials and method of forging. You can make a forged part that is no better than a cast part.

As for why a Quaife most likely ended up in this Cup Car? The forged factory housing cracked in half, as they are known to do, and the previous owner was too cheap or ignorant to replace it with a proper Motorsports grade LSD.

coryf

Thanks for the correction
I updated my post.

coryf

Possibly too much understeer.
With the GT diff you wouldnt have to change anything. It could be setup straight from Matt ready to go.

GTgears

No worries. With some of the low quality forgings coming from the Japanese LSD makers these days I feel it is a very important distinction. One can make incredibly high quality forged parts, which is what Porsche does, for example on many of their suspension components, but certain other companies throw "forged" around as a buzzword to sell things that are practically made out of pot metal.

KaiB

For virtually ALL of our cars!