Plus one on Paul statement- C2s and turbo are totally different in the front geometry.
I must say Doc, -your car looks awesome - congratulations.

 

Slawek you are one guy that knows exactly what i am talking about from your own experiences. Excessively shimming out LFCA's on a 997tt is fraught with problems. And when you look at how many sad stories have been told just here on 6 alone, all associated to "experts" that have had their hands in some of these bilstein issues makes you ask yourself just how much do some of these experts really know. And, just how few have evidently taken the necessary steps to find out the technical ramifications associated to this particular exercise. Having a car look great is one thing but having it stay reliable and in one piece is another. Investigating the association of the drive shaft velocity joint extension limits to the front diff and seal failure, and, the association of neg camber induced by shimminmg gt3 lfcas on a 997tt with the Porsche technicians revealed some very interesting things indeed. Shimming out from the bottom is possible but there are definite limits and it should not to be taken lightly for the sake of a look. There are ways to set these cars up to achieve 2.5 neg and it is evident that a lot of that neg is far better coming from the top than mainly from shimming the bottom. Turning the top strut mounts around will relieve the need for all that shimming on the bottom . That's a trick they use. The other way is to buy some adjustable top mounts but at 2.5 that's not necessary if you do the mount trick. That way only a very small amount of shims need to be used on the bottom, sharing the change more proportionately between top and bottom without extending what little joint limit is most likely left after that 30mm lowering exercise. If you find you need to position the front wheels back out at the top of the gaurd then you're better off using wheel spacers to do that rather than refraining from moving the top of the strut in at the tower.

 

Once again Paul you are correct with your observations and information input.
Over past two years I went through three different sway bars in front -stock,Eibach H&R and back to stock and three different sets of lowering links -Bilsteins, AP's and Tarret .
My first Eibach springs suspension + excessive camber settings on my car, put way to much stress on front axles , sway bar bushings and steering column .After forty minutes of driving on track I needed to stop do to the front axle leakage.I've change bushing on sway bar twice.
It took me over a year to set Bilstein suspension on my car in the way that is everyday drivable, predictable and controllable on the track.We can set this car as low as the GT3RS but this doesn't mine it will drive as one.997 Turbo is four wheel drive and very sensitive in the front.
Doc I'm hoping you are not planing to track your car with the wheel specters on .I still love your car tho,

 

I ran a very similar setup on mine, phenominal on the track.

 

Hi Chris. I recall you saying how yours had the 996 Gt3 Ffca's and the adjustable tarret top mounts, where most of the camber (@1.9 neg) was set up from up top. I recall you said the bottom was very light on shim?

 

Doc,
your car looks awesome!
I have same experience with Paul on this one when mine was set up.

I have about -2.5 in the front on my turbo with GT3 arms. It was done with 8mm shims if my memory is correct and modified top bolt holes to give a little extra up top. The shop that worked on my car said bigger shim is not recommended as they will pull the drive shafts too far out from their slots on the turbo and it will cause problems.
If I ever wanted more camber >-3 in the front, drive shaft spacers are needed. GMG actually makes a pair for our turbo.

All the best!

 

Just went through my invoice again. My car has -2.2 in the front with 8mm shim on the gt3 arms and modified shock tower bolt holes.

 

2.2 is a nice set up. Btw are you using the 996 or 997 lower arms? Also, did they elongate the 3 bolt holes in the towers? I haven't heard that done (not saying it can't be) as reversing the stock mounts produces the most of the required adjustment, but then again many probably aren't aware of that, which is possibly why the adjustable tarret top mount plates are often used. Either way is good though. There is apparently a difference in length between the 996 and 997 arms so that may account for a bit more shim tolerance down there...hence me asking which arms are being used. If your using the 997 ones then less is more again on the shims IYKWIM.

 

Just checked my invoice again and I have 997 arms lol

They have made the holes a little larger so the top hat can move to the sides more to give a little more camber. it serves the same purpose as the adjustable camber plates, but cheaper.
My car had 10mm shims at first, but guys at alignment shop had to take 2mm out to set it up right. we asked -2.5 in the front and only -2.2 was achieved.

Shops that work on a lot of gt3s won't have to deal with this problem. My shop actually called a few shops in the south; GMG was the only one that know about it.

 

Fwiw I have the 997 arms on mine as well. Neg was gained from the top with smallish amount of shims on the lower arms....a nice balance as per Porsches own technical recommendations for that type of set up. What you say about the RWD cars is so true....you don't have the problem with the driveshafts so it's a different ball game in so far as how you approach an alignment with 2+ neg. The problem with our cars is the velocity joints need to maintain the slide movement designed to accommodate for suspension movement and steering angles during driving. Once that movement is reduced by moving the wheel outward from its original position the environment is created for the shafts to slide hammer upon the diff flanges and hub flanges...as the movement of the joints is exhausted and bottoms out. The more the wheel is moved out the less lateral movement the velocity joints have as they simply don't have unlimited movement. The diff flanges are not floating nor are the flanges at the wheel hub end. They are very rigid. Circlips retain the flanges within the diff on the inside end of each splined flange and, at the hub (wheel) end, the opposing driveshaft flanges are even more rigid than at the diff flange end. The sole purpose of the drive shaft velocity joints is to provide the necessary movement for suspension travel and steering angles, which in practice allows these connecting driveshafts to shorten and lengthen through the sliding movement provided within the design of the velocity joints. Once that movement is reduced or removed altogether something has to give up against the slide-hammer effect created from the velocity joints bottoming out and placing pressure against the connecting flanges at either end of the driveshafts. The weakest link in this case is the circlips on the end of the diff flanges inside the diff, and once the circlips yield the flanges are allowed to float in and out of the diff. The consequences are inevitable.

 

Guys here is a pic (not of my car) of front axle driveshaft that may help everyone to understand this a little easier..From it you can see how little side to side travel movement thee is for axle in the differential. If they are pushed out of spec to far the circliips shaft sealing ring may start to leak.

 

From what I was told the 996 GT3 LCAs are shorter then the 997s so you need to use more shim to make up the difference in length, which in turn makes them about the same in the end. i.e. 996 + 16mm shim and 997 + 8mm shim = about the same length. I got mine from Tarett which are 996 GT3 so I would need the larger shim. IIRC we got about -2.0 from the shim and the other -.5 from the top factory adjustment.

I'll look over the alignment paperwork again. I can always get a smaller shim (8 or 10mm) and add more on the top but we are limited to maybe another .3 - .5 on the top from the factory settings.

Thanks for the input.

 

Nope. They are only for the street setup.

 

We only dropped the car 20mm. I didn't want to go any lower.

 

So the big question is does anyone know the difference in length of the 996 to 997 GT3 LCAs?

So your setup is 997 GT3 LCAs with 8mm shims and you've had no issues on the track?