Since I have had an inordinate amount of free time lately, one of the "upgrades" I have been thinking about is an LSD for the 997.1 TT. I first became interested when making this one turn on an uneven pitch from the connecting road, where the inside rear wheel would lift. Unless I was cautious, the inside wheel would suddenly spin before PSM kicked in and slowed the car down to navigate the uneven terrain. Coming from the world of Audi and Torsen differentials, I find this behavior unpleasant.

I have been doing some research and reading over the past couple of days, and after giving some time to allow my brain to fit back into my skull, I though I would post this (I will probably post it on other forums as well).

While I have never tracked the car, I do intend on going to a DE event at some point and I do look forward to spending more time on track where I can experience the car without worrying about a ticket. Even without that desire/goal, I really do not like the electronic approach to managing traction (other than locking the rear in my Quattro when driving out of 12" of snow). I know that LSD was an option on the 997, but during the research I saw many who felt the street option from Porsche wasn't as rugged as kit could be and the race version would actually harm a street driver's performance more than help it. I also read that Guard LSD's seem to have the respect and the real world experience to put them at the top of the list, though there was a spirited back and forth regarding a Giken product. If I had LSD as an option, I would most likely contact Guard (who is now someone else since the well respected Mr. Guard retired some years ago) and have them rebuild one. Since that is not an option I have two tasks in front of me:

1. Decide whether I really want an LSD (my Audi roots says definitely yes, but I am open to opinions here - has anyone else experienced that annoying wheel spin, braking crap??)

2. If "Yes" to #1, which LSD to go with (Guard - seems to be the most well respected, Giken - seems to have gained reputation, Wavetrac or Quaife)

I know that PSM and 4 wheel drive make a difference, but with a stiffer, lower, heaver sway barred car with stiff trans and engine mounts it seems I can do more than the car wants to do right now. At the same time I don't want to be breaking drive shafts or transmissions by trying to "improve" it.

This is a very long term goal, since another item in my research was this was NOT a DIY thing and that the transmission and new LSD would have to sent to a reputable installer to make sure it is shimmed in correctly. That drop will only occur once I have toasted the clutch with a soon to be acquired tune (after dropping my engine I found a brand new clutch so I don't feel like wasting it immediately and I intend to be more careful with a tune and not be too abusive).

Since it is past noon here, time to go drink some of my limited Vodka to help ease my brain swelling, since the State Stores are closed here in PA.

Ed

 

I upgraded my oem LSD to wavetrack but haven't pushed the car yet. If there's a way to check if it's toast or still usable, I can do that and offer up for sale. If you're only doing minor upgrades I don't think you need to go full out with Guard, can just use Wavetrac which is the most popular option I think

 

I have done a full RWD conversion on my 997.1TT. You experience of spinning the inside wheel around corners is ever more pronounced in rwd config. I sent out my diff to get a gt3 lsd put in. I should have the car back this week!

BTW its not just you, using brakes in replacement of LSD is absolute joke. I have a STI and the performance of a real motorsports drivertrain is really amazing. Part of why I switched to RWD in my turbo is because of how much I hated the Porsche awd open diff system.

 

I went with a Porsche Billet Cup LSD (They make 2 versions,.. a cast one,.. (the older versions of which had a cracking issue), and a billet version, as used in the GT1 race car. The latter is the one I have.

Guard was an option, but the friction material is VERY grip'y,... so often you need to keep pulling the LSD back out and playing with ramp rates to get it to work the way you want.

The Porsche material is less grip'y,.. so just tossing the 40/60 ramp rates in there gives you what you're hoping for right off the bat. (40% lock-up on accel,. and 60% on decel)

The Wavetracks supposedly run hot,. and shed a lot of friction material,.. requiring you to drain and re-fill them frequently to get out the yukky mess and smoked lube..

Anyway,.. I pulled my trans and sent it to Brian Copans in Ohio. He does a lot of the trans's for the Porsches at LeMans., (in 2007 , 25 Porsches started the Daytona 24 hours,... he did the trans's in 23 of them) He's also done the trans in 3 LeMans 24 hour winners. http://bmcg-gearbox.com/achieve.html

The raw LSD was $3k I think,.. and about that again for labor. But I also had him refresh a couple of things while he was in there.

It plants power now. I'm making 650 ish at the wheels,... and there's no 1-wheel peels anymore. If it spins them,.. it spins them both. Braking is also less sketchy. Jumping on them from 140 at the track used to cause the rear end to move around a lot. Now from 154,.. it tracks straight.

 

Interesting comment on the wavetrac, I had not heard of that issue, is there a way to know if that is happening?

 

The only way to know if a Diff is dropping material in your transmission is to change the oil in the transmission. You can inspect the magnet on the plug as well as the oil's condition to see if it shows signs of contamination. Alternatively, if you Diff has stopped being a differential, then you can pretty much guarantee there has been material shed into the transmission.

My guess is your driving style will have a great impact on what happens with your diff. Like twisty's and hammering the gas coming out them? You might see more wear.

Ed

 

I'm also interested in where the information posted about Wavetrac diff's having heating issues and releasing debris into the gear oil came from. They don't have clutches to wear out since they are a torque biasing differential, not a true LSD. Since they have a lifetime warranty and are rated for 1000hp if they were having the kinds of issues claimed above they would not be in business anymore. I've had mine for 5 years and it is fantastic for RWD converted cars. After converting to RWD I was very unhappy with the constant intrusion of PSM with it disabled with the dash switch. I put in a separate switch under the hood to cut power the PSM pump and found that I had a 1 wheel drive car once traction was lost just like an old muscle car without some form of posi-traction.
Research on 6SO lead me to the Wavetrac. The first time I experienced a controlled slide after having it installed I had a huge smile on my face. I know the 996 has a far less sophisticated AWD system than the 997 but the concept is the same - without some from of LSD the ECU just cuts power and applied breaks to the wheel that was losing traction. It was terrible. Now it feels like the car should have when it left the factory.
If you're not a serious track junkie the Wavetrac diff is one of the best mods you can make if you have converted to RWD. I have many friends in PCA with all different P-car models running a wavetrac and I have never heard a bad comment about them. I don't normally defend any products but this comment didn't seem fair and I wanted to provide a contrasting point of view based on my personal experience.

 

I'm selling my OEM LSD for $800

 

^^^ What I did is have a used OE option 220 unit (housing) rebuilt with the GT aka Guard internal parts kit. I think you can also use the factory motorsports parts inside if desired.

 

Yep that is one of my options, however an unexpected V10 engine drop will postpone that purchase for a while. Next up will be a tune from Kevin at UMW.

Ed

 

There are other benefits to LSD, but don’t think I ever felt the inside tire spin out happen in lots of track time in a 996TT with awd. It probably happens, but certainly not a constant annoyance as it is in some cars.