^^^^^ Now that's good advice

 

Is there any advantage to a 996 GT3 LSD over a stock 993 LSD?

 

yes, they are night and day, the 996GT3 being much better

 

Bill,

Do you have one in any of your aircooled cars? Anything special to get it to work in a 964 other than having a knowledgeable shop set the backlash, etc.

Mike

 

Bill, how is it better?

 

I have the 996Cup LSD in my car. Very strong and heavy-duty for track use.

 

Still fine for driving on the street I assume? So is the 996Cup or 996GT3 LSD the best solution before going with a Guard LSD?

Mike

 

I have a Porsche Motorsports 40/65 in the G50/30 n my 993, these trans and diffs were oe in the Cup and RSR cars.

993
thru '95 uses a 2 disk 25/65 ZF, the disks were carbon and wore quickly
from '96 thru '98 uses a 25/65 GKN or 22/40, also 2 carbon disks, also used in 993 tt

993RS used 4 disk 40/65 the disks had a sintered surface

the Cup, RSR and GT2 used Motorsports lsd 4 metallic disks

all can be improved w/ GT disks

996 GT3 used a 40/65 GKN w/ 4 sintered disks
the first # is nominal lock up on acceleration, the second nominal lockup on deceleration, both determined by ramp angles

actual breakaway torque is determined by the setup, particularly disk material and preload

 

GT lsds are works of art, they are hugely better in very high torque applications, for those of us w/ normal Porsche power levels the 993Rs, 993 Cup/RSR and 996 GT3 & GT3 cupo diuffs are fine, all the Porsche lsds can be improved by installing GT lamina(disks)

 

Just curious I have a guard 40/60 LSD in my new track car and no speedo. Is there anything that can be fitted to add the speedo pickup? Not needed but always nice to have an idea of speed occasionally.

I was also told the factory housing for the LSD is the same over the years just the internals have changed. Is it possible to fit the internals of a GT3 LSD into a 964 LSD and eliminate the need to adjust the lash on the housing since it will be using the same housing.

 

So, my G50/20 6-Speed has a broken 5th gear.....so might as well change 3-4-5 right? I'm looking at 17" rims, 350+ Hp, DE Track (Tremblant) and road use......any idea of the 'magic' ratios?

 

Morning Gents,

As was mentioned the big advantage of the GT3 LSD is the better ramp angles/higher locking factor. Unfortunately, even with double the clutches, they are still pretty much useless when it comes to tracking a car. See the LSD Buster thread in the 997 GT3 forum for a detail conversation around the factory LSDs. If it were my personal car, I would reclutch it regardless of whether or not it was a 993 or 996 variant.

Tony,

There is a tone ring that provides the speedo drive signal on the 964s. Our LSDs do have the holes drilled in them to mount that ring if you wanted a speedo.

Regarding reclutching your stock 964 LSD? We are no longer servicing those older ones. There are two families of LSDs used in the G50 gearboxes. The early ones, 1987-1995 were made by ZF, like all OEM LSDs back to the 901. Starting in 1995 midway through 993 production, Porsche started working with GKN (the axle company). The LSDs we support are the GKN models.

The reason we no longer support the ZF is age. There are guys out there still trying to race 911 PCA E class cars and 944Spec and all manner of other classes on original factory LSDs. These are 30 year old or older parts!!! The number of LSD housings I've seen fail in the last several years scare me. You break a housing at 140mph in Turn 4 at Daytona in the PCA Club race and you are in the wall. Your car is a write off. Hopefully you can still walk afterwards. No thanks. I'm a motorsports manufacturer and in making parts I need to take racer safety into account. If you are going to spend $40-50k building a racecar, I would hope your life is worth $3000 in cost of putting in a brand new LSD versus trying to limp along on a 30 year old one you "refurbished". You couldn't race on a 30 year old cage would you?

We see 996 GT3 Cup LSD housings break regularly. It's why Porsche went with a billet LSD housing starting 7 year ago on the 997 Cup. The 996 Cup and early 997 Cups do NOT have a housing that is in any way stronger or different than a GT3 street car housing. They are just clutched more aggressively. The last 24 months a lot of my G50 LSD business has been replacing factory Cup LSDs on ones guys are wisely timing out. But keep in mind these are 996 and 997 Cups with a couple hundred hours on them. We always rebuild them, and their street counterparts, a couple times before we toss the whole unit. And we are conservative.

If anyone has a ZF factory LSD you can buy clutches through Porsche Classic. If you have a car you are restoring or just want to drive the same way that it left the factory, you can get ZF clutches at any Porsche dealership. As for my motorsports grade clutches for a ZF? They are NLA.

 

That is good to know. looks like i will be pulling the LSD out of the track car this winter.

The other is just restoring the car the LSD's did not last long the car has only 60k miles. I am assuming the castings crack from fatigue resulting in failure. I am going to do a fluorescent penatrent or mag particle test on the housing before I rebuild it with the factory plates.

Thanks

 

No such thing as one size fits all. Bill has posted some really good options in the past. Search his posts and you should find some comparisons of ratios.

 

As GT says there is no one magic gear stack

the usual knock on /20 for performance is the big gap from 1 to 2 and the tall 3 thru 6

it's a balancing act for a street/track set up, you give up some low rpm cruise for a reasonable spread giving ~165mph top. This ensures some nice close spacing and a reasonable cruise rpm.

I have a g50/30 which was the oe trans in 993Cup and 993RSR. It fits the bill nicely but wouldn't necessarily by doable or best for a modded /20

to save money many guys leave 1 and 2 alone, move 5 to 6 and then fill in w/ new 3,4,5

here is the latest gear stack a friend uses, this is version 2 for him and folows the recipe I outlined above, being version 2 it is an improvement on v1
1 stock 3.818 38mph@6800
2 stock 2.048 71mph@6800
3 1.56 93mph@6800
4 1.241 115mph@6800
5 1.040 139mph@6800
6 .921 stock /20 5th 157mph@6800

this gives a bust cruise 3000rpm#69mph

your torque curve and rpm band will be important in determining what gearing to use

GT is correct I have posted dozens of gearing comparisons