When my JRZ's were ordered, the shaft lenght was designed to the height the car was being set for.

 

So it seems the factory lowered the GT2 the right way to maintain geometry : using lower front wheel carrier mounting points and the previously mentioned 15 MM spacer in the rear suspension arms that " fools " the rear kinematics into thinking that the car is 15MM taller than it rides !

 

Wow Ken... great information!
I am glad that I did not put PSS9's on my car.

 

OK, one at a time........
ebaker,
Yes, raising the ride height would certainly gain me more travel, but that is an artificial constraint I have placed on this project. I want the ride height to stay where it is. I am 100% certain the bump stops are internal within the shock body. The PSS-9's use an inverted shock much like the latest generation of sportbikes. The bump stops are at the very bottom of the shock body. Bilstein told me that the bump stops are progressive so it is not like I am hitting hard rubber but their equivalent spring rate exponentially increases much differently than a true spring. I do not have a cross sectional diagram of the PSS-9's but I am 100% positive they are not external and the Bilstein tech confirmed their presence, type and height with me on the phone.

StephenTi,
I agree, a shorter damper will solve the problem. The ride height is actually within Bilstein's spec believe it or not. It is literally on the lower end of their envolope but nonetheless it IS within their spec. Since my car is on a lift in my garage, it affords me access to the underside very easily. I measured the key point with the Bilstein rep on the phone and we confirmed it was within spec, albeit at the limit. Yes, I am aware that I can cut the bump stops. In actuality, the Bilstein rep offered to do this for me. I would have to remove the dampers, ship them to CA and he would spend about 2 hours at $60/hr to open them up and cut about 15mm off each bump stop. OK, the $120 I can take but removing, reinstalling, realigning, time, effort......ugh. It is an option I haven't completely discounted. In theory, you are correct, the shock body could be threaded. In actuality, it cannot. This is due to Porsche's weird setup (followed by Bilstein) for sway bar droplink attachment. There is a fin plate that is welded to the body to accept the droplink and it is in the way of dropping the damper body any further in the carrier. Why didn't they simply connect the sway bar to the control arm? The torque and bending moment thrown into the shock body fin plate looks so weird!! Maybe the JIC was the way I should have gone.

Curves4S,
I try.

RDH,
Not too low mind you!

David,
See my response to StephenTi.

Tim,
Camber plates......yeah, I know, but upon further consideration with Gary and some realizations that came to bear during my discussion with him, the only way they would increase the travel is if they were specifically machined in a manner that locked off the center pistion shaft nut at a higher elevation than the strut assembly-to-body mounting plane. They would resemble a volcano in cross section for this to work. They are not made like that, although a custom machined fabrication may work.....hmmmm.

james,
As I said, I spoke with the Bilstein tech. The bump stop is internal and can be modified to a small degre, by them, and with a loss of warranty. No such thing as a free lunch!! I WISH TO STATE FOR THE RECORD, THIS IS NOT A PSS-9 BASHING SESSION. THEY ARE A GREAT PRODUCT AND THEY WILL WORK FANTASTICALLY WELL FOR MANY!! I AM GROUPED INTO A MINORITY WHEREIN THE OUTER, OR IS IT LOWER LIMITS ARE BEING EXPLORED. I AM NOT DISSATISFIED WITH THE PSS-9's AS A PRODUCT.
I think the stiffer spring scenario you menation is one possible solution. The overall droop is what takes away travel. THe droop is made up of unloaded to staticall loaded compression of some proportion of the tender and main springs. The tender springs are simply there to keep the main springs seated during unweighting. If I can change the proportion of the uncompressed height between the main and tender springs, I buy back travel. As an example, install a 1 inch taller and stiffer main spring. Remove 1" of the tender spring from its compressed length. I have now added 1 inch of travel!! Voila! I intend to talk to Bilstein about this. Stay tuned.
Inceidentally, the bump steer kit addresses the STR but not the CA.

03-turbo911,
The RUF setup diefferences I know of are as follows:

• Different spring rates (assumed stiffer)
• Different valving (assumed more aggressive)
• Less negative camber in front and rear wheels for better high speed Autobahn response.

One of these days, I will pay to have Sean's car put on the rack to see his alignment settings.

cjv,
The shorter JRZ's solved the travel issue but what was done for the STR and CA angles? I didn't have a chance to call Rob the day after we spoke. I will call next week.

MKW,
YES!!! At least I think so. I am still waiting to see if the GT2 front wheel carrier in fact has lower pick-up points for the STR, CA and SB. I have two people checking into this. If anyone knows the part number for the GT2 front wheel carrier, please provide.

Dougie,
Oh no!! Again, this is not a PSS-9 bashing party!!! They work and work well, WITHIN THEIR PRESCRIBED LIMITATIONS!!!!!
I think others will agree with that.

 

Did you consider the 7x7 way adjustable Moton racing shocks, these are considered the ultimate suspension ugrade for track bound GT2 & 3's.

The good thing with these is you can have them pretty much made to spec.

Try this guy, I have spoken with him on several occasions, he knows his stuff really well, and may well be of help.

Steve Weiner
Rennsport Systems
Portland, Oregon
503.244.0990
E-mail: porsche@rennsportsystems.com

 

Macfly,
If I end up changing out the suspension, I will go with the Motons. I already have a proposal for them. I agree, they are supposed to be the cat's meow.
As I mentioned, I have talked at length with Steve Weiner (See my original post). Yes, I agree, he is a great guy and very knowledgable. The Porsche world is very small it seems.

Incidentally.....I was speaking with Rockitman while perusing a website last night and must say, from one amateur photographer (me) to one pro (you), you are my hero!!

 

Thanks for the great post Ken. How do I learn more about Moton? Anyone have a link for the company. I couldn't fine one.

 

http://www.motonsuspension.com/

 

Thanks again

 

Ken,
any comment or insight on the OEM X73 suspension since it's factory approved?

 

Arling,
I have a few beliefs and comments to share about the X73, nothing bad mind you, but before I share them, I would like to know what the ride height specification is for the X73 spring/damper set. I have the values for the USA Turbo, ROW Turbo and GT2. Can you provide the X73 ride height spec to me?

 

Overall Droop has nothing to do with the lack of suspension travel that you are experiencing. As you had stated, droop is "made up of unloaded to staticall loaded compression of some proportion of the tender and main springs." However, at loaded static height, the ratio of main vs tender is irrelevant to suspension travel because as long as you intend on keeping your ride height, the loaded (main + tender) distance is a constant, not variable.

So, let's take the extreme... we'll make your tender springs infinitely short (basically, take it out), and make your entire droop all main spring. Now, when you lower your car, yes, you'll have gained suspension travel, BUT, it is because you've also consequentially raised the ride height of the suspension. When you go to reduce the ride height back to where you originally want it, you're car will be right back on the previous bump stops. Make sense?

If your car has 2" of suspension travel before bump stops prior to lowering, and you want to preserve this while lowering your car 1", then you must have damper bodies that are 1" shorter than the original damper bodies (or stops). To say it another way, if you want to get more specific, you must maintain the distance between the distance as measured from the top of damper travel to bottom of damper travel as previously. You can change the ratio of tender vs. main spring ratios all day long, and it won't make a difference.

Again, this is assuming that the shock body is not thread-able below it's suspension mounting point, which is what I had previously eluded to. One of the main advantages of the JIC design is that the shock body can be threaded relatively to the knuckle, which allows for you to adjust ride height without affecting suspension travel.

In coilover designs where one can not thread the damper body relatively to the suspension pickup (knuckle in our case), the only way to lower it is to lowered the lower-spring perch. Anytime you do this, you are taking away suspension travel. There is no way around it. To compensate, some will cut the bump stops. Because most bump stops are not linear, there will be a huge jump in combined spring rates of spring+bumpstops when they bottom out.

Now, in JIC's design, visualize that the lower spring height, once set, will never have to move relative to it's location in space. You can take away or put bak suspension travel by merely threading the damper body up and down.

I'm not pushing JIC, as I've my own issues with my setup. But it's clear why one design is better than the other in addressing the issue on hand.

 

Stephen,
Thanks for keeping me honest here!

In actuality, I am usually much sharper than that! All of this information, and thought processing has made me a bit numb. Sorry about that! I concur regarding the ride height/shock travel/spring stiffness proportions.

Please explain the JIC design further.

 

Stephen,
By the way, what is your background?

 

Not at all, Ken... I always find useful info in your posts, and knowledge sharing is what this is about.

I've edited my previous post to try to explain the difference in the two setups better (not to mention taking out gram/spelling errors ... my brain was a little slow this AM too). Check it out, and reply with any additional questions.

As for what I do... I guess I can say I'm currently in realestate. I was in IT for many years (ever heard of Lucent... yikes). Got into some realestate briefly, then med management biz, and now, I'm just starting to get back into realestate. My degree is in IT, though I was 16 hrs from an Industrial Eng BA.

But, that's all irrevelant, because I'd imagine as with you guys, most of my schooling was in life. I've been reading car mags since I was a kid, and have always done as much of my own wrenching and research that I can get my hands on. If only I got paid for this hobby, I'd be filthy rich. Instead, it just drains my pockets!