cannga:
For those following this thread and new to suspension mods, let me summarize what I've learned in case you are interested. There are 4 common mods that people have added to the Turbo, with number 4 probably the least frequent:
1. Front camber adjustment to reduce push/understeer. Stock is -.4 or so, a common target is about -1.3.
2. Lowering and stiffening the car. 2 ways to do this: With coilover such as Bilstein, or lowering springs...
3. Stiffer Anti-Roll Bar (the drop links that connect the anti-roll bar to the suspension are sometimes also replaced).
When I posted the above 7 months ago, someone (Alex) asked the very valid question that, which of the top 2 changes, Bilstein versus alignment changes, is responsible for the dramatic improvement in the Turbo’s behavior. At the time, I said Bilstein, which now seems to me like the wrong answer, or at least the wrong way to approach that very good question.
In retrospect, the simplistic answer I gave, that Bilstein was the "star" of the show, was partially wrong for the following reason: you can’t really compare the 2 modifications because they affect 2 different aspects of a car’s handling, which are, a. overall body/chassis control (Bilstein), and b. cornering and turn-in behavior (alignment changes). As always, I don’t claim to be a professional, just sharing amateur-level experience here:
Bilstein: When you accelerate, the stock Turbo’s squats; when you brake, it dives; in corners, it leans and its rear end has vertical & lateral motions. The Bilstein helps to control these motions, which to my thinking are related to the car’s body controls, in corners obviously, but majority of the times, it involves “straight line” behavior.
Alignment Changes: To me, alignment changes affect more or less the car’s behavior in corners. How the front of the car turns in corner (understeer), how the front responds to steering input (turn-in response), and how the rear end rotates.
If you are new to this and have some trouble understand what I am talking about, I encourage you to take test drives in the C2, or any RWD Porsche. (I love comparison drives; they have been critical to my learning.) I think your experience would match my observations below:
1. The Turbo, as set up from the factory, understeers. It is beyond the scope of this post to explain in nit picking details, but basically if you approach a corner at speed, the nose wants to go straight. To me, the Turbo does this more than both the C2S and the GT2 that I’ve driven.
2. Turn-in behavior: The steering of the Turbo is stubbornly straight. The good thing: Great & solid center feel. The bad thing: If you move from center, it wants to go back straight. This is different, in a bad way IMHO, from both the C2S and the GT2 that I’ve driven.
3. Rear end rotation: It is extremely hard, actually impossible, to get the rear end to rotate in stock form. The car just wants to go straight. It is safe behavior and I understand why Porsche set up the car this way, but personally I would prefer more rear end rotation.
The 2 alignment changes that I have made to my car are: increasing negative front camber to minus 1.2 degree, and change the front toe setting from toe-in to slight toe-out at minus 0.02 degree. The first change (front negative camber) is common among enthusiasts, but the second (front toe out) I’ve only seen in race/GT3 forum, and is used for selected drivers by (at least) some very well known tuners here in Southern California, including mine. My tuner (a great and very careful one) was hesitant to do the toe-out for me, probably because I don't track and I am only a beginner level driver, but I "pushed" him towards it because I was curious and wanted to learn, with the idea that I will set the toe back to factory level eventually. As it turns out, there are pluses and minuses, but I am now having second thoughts about going back to the factory toe level at all and I do "get" what the tuners and track guys are trying to do with this setting.
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Regards,
Can
997 Turbo + Bilstein PSS10 (Review) + Cargraphic Exhaust (Heavenly Race Car Noise Review)