Let me start by giving some details on my car. I have Bilstein PSS10's and a rear GT3 adjustable sway bar (so I was told). After driving the car I knew I was going to need more rear bar and potentially stiffer rear springs. My rear swaybar has 4 holes in it and is currently set in the 2nd hole (the next to softest setting).

My car has good turn in, but just doesn't have the balance of my old Supra and current E46 M3 (both cars have aftermarket suspensions and have done track time). I don't want a brutal track suspension, but when I looked at some specs for a 997 GT3 RS, the spring rates seemed very reasonable.

This got me thinking. If I use the specs from the GT3 RS and compare it to my car, will this allow me to have a similar feel/ride with my car. I'm sure I'll never get the steering feel and my turbo weighs more, but if I could just get the balance.

Below is the start at accumulating the data.

If you have any of the GT3 RS data that is blank, let me know. If you see some incorrect data for either car, let me know. Most of the 996 data should be correct, as I spent this morning measuring everything on my car. The motion ratio and spring angle may be different on the GT3 RS since I believe the suspensions components are different, but I simply used my 996 information as it should be close. Again, let me know if you have more accurate data.

If the front swaybar on the GT3 RS is similar to my car than it looks like some stiffer rear springs and new rear drop links (so I can get the rear swaybar set to it's stiffest setting as it currently hits the toe links in the two stiffest settings) may be all I need. Apparently the PSS10's have appropriate valving to handle up to a 700lb. spring, so I shouldn't need to change the valving.

Here is the data.

Later, Steve

 

Does anyone at least have the diameter of the stock 996 TT swaybars?

 

I just found this and it was very helpful.

 

Steve,

I installed the complete RSS Tarmac series setup on my car, made a world of difference on how direct and stable the car became. Was also surprisingly comfortable on the street (roads here are terrible).

Tires will thank you as well, was destroying them from all the toe movement that the stock rubber bits provide.

 

Well you have have a few problems with your plan.
1) GT3 rs is lighter
2) GT3 rs has relocated pick up points for the arms/linkage
3) GT3 rs is rear wheel drive only
4) turbo car squats more the GT3 rs under acceleration

 

1. Not by as much as you think. Approximately 200lbs, which I'm accounting for in my calculations.
2. Again this will be accounted for in the calculations. I have a GT3 RS close to me, so I will measure and collect the data myself.
3. Agreed, but the weight distribution is very similar and I'm talking about steady state cornering.
4. Again, I'm talking about steady state cornering.

Later, Steve

 

GT3 FRONT:

996.1 GT3
PART NUMBER: 996 343 531 91
SPRING RATE: 35N/mm

996.2 GT3
PART NUMBER: 996 343 531 95
SPRING RATE: 40N/mm

996.2 GT3 RS
PART NUMBER: 996 343 531 97
SPRING RATE: 45N/mM

997.1 GT3
PART NUMBER: 996 343 531 95
SPRING RATE: 40N/mm

997.2 GT3
PART NUMBER: 997 343 531 94
SPRING RATE: 49N/mm



GT3 REAR:

996.1 GT3
PART NUMBER: 996 333 531 91
SPRING RATE: 65N/mm

996.2 GT3
PART NUMBER: 996 333 531 95
SPRING RATE: 95N/mm

996.2 GT3 RS
PART NUMBER: 996 333 531 95
SPRING RATE: 95N/mm

997.1 GT3
PART NUMBER: 997 333 531 93
SPRING RATE: 105N/mm

997.2 GT3
PART NUMBER: 997 333 531 95
SPRING RATE: 115N/mm

´06- 997 CUP:
Fmain length mm - N/mm: 100-260 997.343.531.90
Ftender length mm - N/mm : 75–43 996.343.537.90
Rmain length mm - N/mm: 130-260 996.333.531.90
Rtender length mm - N/mm: 60-50 996.333.537.90

996 turbo:
Running gear
Front axle Spring strut axle Wheels individually suspended by control arms with
trailing arms and spring struts (McPherson design,
optimised by Porsche)
Springs One truncated cone spring per wheel, with vibration
damper inside spring
Spring constant 33 N/mm
Spring wire diameter 12.6 to 14.0 mm (in)
Coil diameter 113.2 to 186.5 (3.6 to
7.35)
mm (in)
No. of turns 4.05
Stabilizer diameter 23.6 x 3.5 mm (in) tube−type stabilizer
Vibration damper Double−acting hydraulic twin−tube gas−filled vibration damper
Rear axle Multi−link axle
Wheel suspension Wheels individually guided by 5 control arms
Springs Cylindrical coil spring per wheel, with coaxial vibration damper inside spring
Spring constant 60 N/mm
Spring wire diameter 13.21/13.35 mm (in)
Coil diameter 115.0 mm (in)
No. of turns 6.75/7.0
Stabilizer diameter 21.7 x 3.0 mm (in) tube−type stabilizer
Vibration damper Double−acting hydraulic single−tube gas−filled vibration damper

 

Interesting, I thought the stock 996 turbo rear swaybar was a solid bar. Given this, it appears to be tubular.

Also, is the 3.0mm listed below the wall thickness of the tubular swaybar?

"Stabilizer diameter 21.7 x 3.0 mm (in) tube−type stabilizer"

Not to be greedy, but do you have the 997.1 GT3 RS info?

Thanks for the great info,
Steve

 

First let's be more specific than you don't like the balance, what exactly is the car doing in steady state cornering? Sounds like understeer if you are talking about stiffer rear springs.


4) Steady state is where the difference between RWD and AWD is the most apparent. None of the other cars you mention have AWD or have to cope with power understeer. The experience will be totally different.

 

The car turns in reasonable well, but immediately goes to understeer at the limit.

I'm not talking about power on accelerating through the apex, where I would expect the awd to start trying to add power to the front wheels and causing understeer.

I think you can easily look at the front to rear wheel rate and understand why a car with over 50% on the front and only 38% of the weight on the front would understeer. Regarless of awd or rwd.

Later, Steve

 

Agreed, which is why 911's have mostly understeered at the limit, especially the 996. Push though is affected by weight distribution and is easier to remedy, power understeer is available at all times, especially steady state, and even more off camber steady state. GT3' s do it too. The best route is changing camber, then rake, and then playing with the bars and springs. 996 TT has power to wheels at all times so the longer you are turning, the more you notice it. Some of that never goes away with awd.

 

I just added tarret camber plates up front in lieu of the stock units and have ps10's and adj ft/rr bars and control arms among other bits for suspension.

While adding the camber plates I had the ft raised .25 inches bc my aero lip kept scraping. Amazing what just that rake change did because now I am feeling more push than what I had prior even though I went from -2.7 ft and -2.3 rear camber to -3 ft and -2.6 rear.

I think now I have zero rake and the car though it is lowered a tad from stock but sits even now had a better crisper turn in when I had .5 inches rake and even .25 inches rake.

HR bar ft is full soft and rear full stiff. PS10's are full stiff rear and 6-7 clicks to stiff ft. My next step is to further soften the ft coilovers to 4 or 5 and see if that helps.

 

If that does not help, then I will likely have to build back in at least the .25 inches of rake or more but the more I go the closer I feel I start hitting the bump stops up front and obviously tearing up the aero lip. Good thing it is oem so poly instead of the hard stuff.

 

Yes, rake > camber when it comes to handling which is why I say to try and find the camber settings first because it can be negated by small rake changes. I had the same issue with my splitter bottoming out, but my car is really low. What we did was raise the front until it stopped scraping and then raise the rear until I got the handling back. Overall ride height is not as big of a deal as the rake itself.

 

Rake is the answer. toe out up front-- a splitter up front as well.

I use to get under steer only at high speed bends, after splitter that went away. Iv always have gotten over steer at low and med turns, with my alignment settings.