I have heard of this Walter Rohrl guy I think. Not a bad driver from what I am told but I am sure I can teach him some Rally Driving Skillzzzz.

 

very nice choice i must say !!!!

 

I have been looking for the shock dyno curves for the Bilstein coilover for a long time, finally found one on Bilstein Germany's web site -- duh. Unfortunately, I only found the one for the PSS10 version, not the PASM compatible version, aka Damptronic, so you see 10 curves, not 2. I've been told that the Damptronic uses the softest and stiffest curves for its 2 settings, with other adjustments made as the car sense the road and your driving, etc., but this is from Bilstein USA Help Desk, not official documents from Bilstein Germany itself.

In case you are curious how the shock dyno curves correlate with your driving, and to understand how coilovers differ, some more amateur level info:
The horizontal axis is the speed of the piston shaft. Events such as acceleration, cornering and braking cause slow compression of the spring/shaft, as your car squats, leans, or dives. This is referred to as low speed bump (bump = compression, not a bump on the road). To my thinking, this is related to the "good" effect of stiffer suspension -- the sporty handling.
OTOH, when you hit a curb or pothole, the spring and piston shaft is compressed at high speed, also known as, of course, high speed bump. This is related to the bad effect of stiffer spring -- the harsh ride.

This curve illustrates why for most amateurs, the Bilstein Damptronic version, where damping forces are automatically set, are so much more desireable than coilover where you have to set damping forces manually. Why? Even though in theory the manual setting of damping forces are more desirable, I can't tell you the number of times I've seen owners lost as to the why/how of damping force setting and never found the "Holy Grail." Manual setting of shock absorber damping is TOTAL black art reserved for the most advanced of drivers and setup people. Driver must be able to give feedback to setup man (understeer vs. oversteer, compliance), and setup man must know what to change for desirable result. I know certain suspension web site states just set up so and so for comfort and so and so for handling, but in reality this is NEVER this simple because whatever you do to increase comfort, will cause handling to suffer.


I've marked the graph using values from this excellent article -- written by, of all people, an anesthesiologist and a radiologist.
http://www.pca.org/panorama/sample_article_3.html
The KW Variant 3 coilover for example, allows one to adjust low speed bump; whereas a 4 Way Adjustable Moton allows adjustments of low speed bump (aka compression), high speed bump, low speed rebound, and high speed rebound. As mentioned, from my reading of past postings, simply spending mega $ for a sophisticated 4 way Moton definitely does not guarantee happiness. It should be reserved for experienced & very advanced level drivers and tuners. I believe that for a majority of amateur drivers, the simple Damptronic might actually be the best.

 

I would have to agree with Can. Buying the most expensive or best system does not equate to performance. It really does take a great tuner to setup a system right. It took 3 tuners for me before I was really happy with my setup. BBI in Huntington Beach was the only shop that was able to set the car up correctly. Their experience in ALMS really shined through here.

It's crazy to think that it took 3 different tuners to get it right. I am finally happy now. It was a long and frustrating process, but the car is really planted now. The turn ins are crisp and body roll is non-exsistent. The rear end twitch in high speed turns is pretty much gone. The ride quality is a bit stiff, but that doesn't bother me. As Can said, I think the PSS10 might be the best setup for the average weekend warrior. Full adjustablility like my JRZ's or Motons might not be the answer and probably complicates things more. I don't think most people will have the patience to go through what I did.

 

And the adventure continues . Up next: the effect of front negative camber and front toe-out. (Please note: I am NOT recommending this to anyone, merely describing my experiment/experience.)

When I posted the above 7 months ago, someone 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, affect mainly the car’s behavior in corners. How the front of the car turns in corner (understeer/oversteer), 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.

Subjectively, the result of 1-3 above is that the car feels un-natural and a little "dead" (as in not "alive" ) when it enters a curve. It doesn't follow the curve, instead wanting to go straight, and perhaps as result, it leans a lot. In addition, when you apply throttle coming out of a curve, the rear end doesn't rotate so it's so much harder to perform a power slide (am sort of kidding with this last one).

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 racing/GT3 forums, 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 (toe in) at all and I do "get" what the tuners and track guys are trying to do with this setting.

The car now feels "alive" , when you move the steering wheel, the car responds and turns quickly, and has more willingness to turn, and the car's body & rear end rotates nicely to follow the curve. (BTW, another very noticeable effect is the steering wheel effort now feels much lighter.) IMHO the alignment change makes the car much more similar to the GT2 when it comes to turn-in response (very quick and responsive in the GT2) and corner behavior. It is now so much more fun on twisty roads and feels very fast and responsive. True also, as it feels more sporty, it also has become more edgy: There are 2 curves, a 43 mph and a 71 mph one, that I've done hundreds of times as they are on my way to work; I am now perhaps faster in the 43 curve because the car appears to lean less but slower in the 71 just because, like the GT2, it feels like you have to pay attention at the edge or the thing is going to give, and I get scared easily.

 

Some reading material if you are interested:

http://www.ozebiz.com.au/racetech/theory/align.html
....If the car is set up with toe-out, however, the front wheels are aligned so that slight disturbances cause the wheel pair to assume rolling directions that do describe a turn. Any minute steering angle beyond the perfectly centered position will cause the inner wheel to steer in a tighter turn radius than the outer wheel. Thus, the car will always be trying to enter a turn, rather than maintaining a straight line of travel. So it's clear that toe-out encourages the initiation of a turn, while toe-in discourages it.
....The toe setting on a particular car becomes a tradeoff between the straight-line stability afforded by toe-in and the quick steering response promoted by toe-out. Nobody wants their street car to constantly wander over tar strips-the never-ending steering corrections required would drive anyone batty. But racers are willing to sacrifice a bit of stability on the straightaway for a sharper turn-in to the corners. So street cars are generally set up with toe-in, while race cars are often set up with toe-out.

http://www.mgf.ultimatemg.com/group2/suspension/toe.htm
...If the car is set up with toe-out, however, the front wheels are aligned so that slight disturbances cause the wheel pair to assume rolling directions that do describe a turn. Any minute steering angle beyond the perfectly centered position will cause the inner wheel to steer in a tighter turn radius than the outer wheel. Thus, the car will always be trying to enter a turn, rather than maintaining a straight line of travel. So it's clear that toe-out encourages the initiation of a turn, while toe-in discourages it.

 

Now, if we add your alignment to the new PSS10 Springs set up, i am sure it will make a big difference.
As you noted that the car wants to go strait and when you turn it still wants to go strait, i learned from working on my C6, even though a different animal, i am having to stiffen the front springs in order to have more grip and better direction, on the other hand, stiffer rear on the 997TT will provide a much better and more "ALIVE" cornering as long as it is done with respect to the front end as well.

Love the review, will keep you posted.

 

KA, thanks.
I should also add that it's now a little hard for me to tell which one does what as far as front negative camber versus front toe-out alignment change, but it seems the front camber change reduces understeer, while the front toe out is what causes the steering to become so much more fun & responsive.

 

That's a masterful thesis you got going cannga! Very well written and makes it easy to understand to those not familiar with how these cars operate. I'd also want to be careful with the toe-out, it can makes the car unstable and for the novice, it can be quite a handfull! The rotation is increased though and it makes it flow better from corner to corner.

 

Maraheb Khalid,

Thank you for the insight on this, I am going to give his specs a shot and see what I will come up with.

 

Marhaba!

Lived nearly nine years in Austin during the 80's! really miss it.

 

Can - Car went in for surgery today . I opted for the Gt3 alignment spec . My guess is the car will handle better but the negative camber may place a bit if wear on the tires . That's ok ... all in the name of peformance .

With the Gt2 sway bars also going on as well as my other mods I have a feeling within aboit 10 days of getting my car back I will have a better opinion .

This thread has been very helpful. Thanks.

 

Great write up Can. I know exactly what you are talking about when you compare the 43 mph and 71 mph turns. My recent changes in the setup really got rid of a lot of that rear end twitch. Higher rebound in the rear with increases in rear toe in to 4.5, front toe out to 1, front camber to -1.9, and rear stiff for the sways and neutral front really did some wonders. I can''t say exactly which one thing or things did the most, but it seems to work.

 

Hey guys, thanks for the encouragement & kind words. I really have spent way too much time reading, testing, probing (the vendors who don't like to talk :-)), and learning from others; it feels very good to have the result recognized by fellow Porsche nuts.

As mentioned in the other forum, I am definitely coming towards the end of modding my suspension; from now on it's more or less tinkering about for the sake of playing around, as the key work has been done (I think -- grin). As you could tell, despite of much "talking," the changes I've made are rather conservative and minimal -- the 3 small steps to Nirvana LOL. In return what I have is a car that is still close in spirit to the original Turbo (daily driver), yet night and day more aggressive in nature: A ferociously fast beast with a nuclear power plant for an engine, and handling and chassis dynamics to match. I know my adventure has been successful because I do miss my car very much every couple days that I don't drive it.

BTW, enclosed is a comparison table of stock settings, plus the two simple alignment changes I've talked about. Watch the units, some are in degree, some in minute. eg -1.2 degree = 1 degree 12 minutes.

 

I took your advise and revised the alignment, huge difference, you are welcome to read my write up on swaping the PSS10's.
https://www.6speedonline.com/forums/...ails-pics.html