viperbob

I was wondering how other 993TT owners with the PSS9 upgrade think of the overall stiffness with the springs provided by Bilstein? I have my shocks set on 1 (stiffest) in the rear and 2 up front. With this setup, my car seems to handle fine on the turns. However, when my car accelerates, I get a lot of either rear end squat or front nose coming up (not sure which). Braking of course is just the opposite. There seems to be an excessive amount of travel here. Has anyone that has made engine performance modifications seen the need to install stiffer springs? If so, what types of springs and spring rates did you install?

Thanks

Anir

Bob,

It sounds like your car is coming along nicely.

Personally, I have not noticed excessive squat or dive with the PSS-9's, but have only done one Mid Ohio DE event with them (settings 3 front / 2 rear). On the street, I run about 6-8, because I feel like the fillings in my teeth will otherwise come loose.

Certainly, the springs are soft (on paper) compared to more dedicated track springs, or even the springs with the H&R supercup coilovers.

I'll pay closer attention to the issue at Road America this weekend.

djimenez993tt

Bob,

I have mine on number 9 (soft) and I feel that it a bit jarring on our mexican streets. I do have to point out that when I use the car in your USA highways the ride settles down and feels more 996'ish.

I have almost no squat, nor dive. are you sure you have them set in 1? I had a hard time knowing whichh was which, I had to call the Bilstein rep. here in mexico.

But then again, mine are the Ruf setup, which are supposed to have custom valving and spring rates.

viperbob

Anir and David,

I am having the problem as the turbo boost is coming on quick and hard. Yes the shocks are set to 1R and 2F. When I had the Unichip setup, it was dyno'd at 507HP, and it really didn't have this noticable a problem. It is much faster now with the new intercooler and Protomotive ECU setup. I know David you have the X50 option which should give you Turbo S HP I believe. I am wondering if the extra power now is over powering the standard PSS9s setup. Do you know David what the spring rate RUF uses? What am I saying? The only things not secret with RUF is there name, and they are headquartered in Germany.

Any other thoughts would be appreciated...

Anir

Bob,

Perhaps, your significantly greater power is overwhelming the suspension on hard acceleration, but this should not be an issue with braking (i.e. dive), right? We're all running Big Reds.

djimenez993tt

Bob,

No idea what so ever, Sorry.

You know, thinking it over, my car does squat when I accelerate hard in abrasive streets, the streets here are not abrasive at all, you can go thru a set of tires without wearing them down, you know they are gone by the hardness of the rubber.

But my squat aint that much, and I would blame it on my 9 settings, I haven't even tried some other setting, the streets are so awfull here, I dont dare to do it.

Wish you luck! I'll try to find out with Asgar tomorrow, hope he knows and if he is willing to share the info. Asgar! Are you reading this?! Help needed here!

ZCAT3

Hi Bob - our 993TT is about 520HP and we do not get any significant squat under hard acceleration (unlike our 930). Our suspension is the M030 ROW suspension set to RS ride height (as far as I can tell at least). One thing that makes these cars squat a lot less is the AWD system. Under full throttle acceleration with over 500HP I would expect that a fair amount of power is being sent to the front to maximize traction. Maybe TRG disconnected your AWD? I am just kidding (I hope).

viperbob

Thanks guys. Maybe I am just being over sensitive. And Bill, you do have me thinking and I will check to see if they left the AWD disconnected after the last dyno run (still do not have my cruise control cable after it was broken during the upgrades. They tell me it is on back order from Germany. That has been 7 weeks now).

Maybe I'll take it to Laguna Seca on Friday and see how it does on the track.

TB993tt

Bob
I have just had my solid top mounts removed, standard rubber ones put on the front with Steve Ws mounts in the rear had PSS9s fitted and set on full soft. I am trying to drive my car more, including taking my 2 Y/O in the back so trying to "soften" it up a little. I find the PSS9s pretty harsh at low speeds (on bad UK roads)- I wouldn't want the springing any harder. As for the squat issue, can't say I notice any even when 560lb/ft comes in, I have noticed more, what I would call "twisting", a feeling that the car is trying to jump off the road, (when the torque comes in) but presume this is more to do with the top mounts.
ZCAT
I understood that the 4 wheel drive system feeds 5% torque to front under normal driving and only delivers more when there is actually rear tyre slippage, so unless you are actually lighting the rears up under acceleration, you are only getting that 5% to the front. What I like about this system is if you powerslide the rear out, the torque is sent to the front and makes the car much more controlable, nicely straighting up - makes you look like an "ace" driver <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

johnfm

TB993TT

you mention your car 'twisting'. Could this be torque steer from incorrect kinematic toe?? There is/was a very interesting kinematic toe thread on the 993 board, BTW.

re: your 2 YO - my 5 YO and 7 YO LOVE riding in the back of the C2, but roads in Leeds & my driving makes it qute fun for them!

JohnM

TB, the "twisting" is more likely to be the (in my opinion) entirely inadequate damping the PSS-9 has on full soft. Back end moves around a lot with PSS-9 at the softer end of its range. The car gets much, much better if you set the dampers on 6 (or stiffer), but granted the ride is firmer. With the torque your car puts out it might get somewhat more entertaining than it must usually be if you make any fast direction changes with soft settings

John H. in DC Area

Bob, I thought your issue sounded vaguely familiar, and I just now realized from where. Your issue may or may not be related to this, but here's an excerpt from the May 2003 Excellence mag featuring the Ruf CTR and CTR2 (993-based). The article notes some handling and dive/squat issues stemming from the impact of high torque levels on suspension bushings:

Excellence, May 2003, pp.95-96:

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"><strong> The Stock rear suspension bushings wind themselves up and try to spit the rear end of the car off-line at every opportunity. You see, Alois Ruf is concerned with ride comfort as well as good handling and this, he says, is the reason he does not use more exotic bushings in the 993-based Turbo R and CTR2.

Unfortunately, his fabulous engines are able to produce more than enough torque to wind the factory bushings to the limit under hard acceleration. Of course, this affects the geometrical behavior of the rear end, producing a distinctly unsettling feeling. But I'm not alone in my observation: Autocar drivers in a track test at Silverstone reported wayward handling. Road & Track's Mario Andretti also noted high-speed instability, but later said tie rods damaged in shipping were the culprit.

Between the Ruf CTR and CTR2, the Carrera that served as the basis for the CTRs fundamentally changed -- twice. The first redesign (964) went to MacPherson-strut front suspension and coil springs at the rear as well. But the CTR series jumped a generation, so the newer CTR2 was based on the subsequent 993-generation Carrera, with its rear suspension mounted on an alloy subframe that is then bolted to the rear chassis section.

Isolation from road shock is the main reason for this setup and the system does a great job of removing the road noise and vibration that afflicted earlier 911s. Unfortunately, this design has one problem, which centers around elastokinematics -- the science of the relationship between the vertical and horizontal movements in a suspension system. It's only when you introduce very high levels of power -- and well over 500 hp and lb-ft is certainly enough -- that problems arise. The added torque compresses the bushings fully and very quickly under hard accerlation, changing the rear axle geometry on the move and making for some rather unpleasant handling traits.

Porsche was well aware of this potential problem and stiffened the rear suspension bushings of the most purposeful 993s, the Carrera RS and GT2, also known as 911 GT. Apart from homologation of these parts for competition, they also keep these very powerful cars pointing straight down the road no matter how much power you feed in -- and the difference in precision is staggering. Porsch engineers say that, if you stiffen up the lateral bushing enough to contain excessive movement, you can afford to make the spring and shock rates softer in the vertical plan to take the edge off short, sharp bumps. Of course, this is a Porsche problem that added power only accentuates and a CTR2 with the harder rear suspension bushings achieves near perfection.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Don't know if this helps. Good luck.

TB993tt

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by John H. in DC Area:
<strong>Bob, I thought your issue sounded vaguely familiar, and I just now realized from where. Your issue may or may not be related to this, but here's an excerpt from the May 2003 Excellence mag featuring the Ruf CTR and CTR2 (993-based). The article notes some handling and dive/squat issues stemming from the impact of high torque levels on suspension bushings:

Excellence, May 2003, pp.95-96:

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"><strong> The Stock rear suspension bushings wind themselves up and try to spit the rear end of the car off-line at every opportunity. You see, Alois Ruf is concerned with ride comfort as well as good handling and this, he says, is the reason he does not use more exotic bushings in the 993-based Turbo R and CTR2.

Unfortunately, his fabulous engines are able to produce more than enough torque to wind the factory bushings to the limit under hard acceleration. Of course, this affects the geometrical behavior of the rear end, producing a distinctly unsettling feeling. But I'm not alone in my observation: Autocar drivers in a track test at Silverstone reported wayward handling. Road & Track's Mario Andretti also noted high-speed instability, but later said tie rods damaged in shipping were the culprit.

Between the Ruf CTR and CTR2, the Carrera that served as the basis for the CTRs fundamentally changed -- twice. The first redesign (964) went to MacPherson-strut front suspension and coil springs at the rear as well. But the CTR series jumped a generation, so the newer CTR2 was based on the subsequent 993-generation Carrera, with its rear suspension mounted on an alloy subframe that is then bolted to the rear chassis section.

Isolation from road shock is the main reason for this setup and the system does a great job of removing the road noise and vibration that afflicted earlier 911s. Unfortunately, this design has one problem, which centers around elastokinematics -- the science of the relationship between the vetical and horizontal movements in a suspension system. It's only when you introduce very high levels of power -- and well over 500 hp and lb-ft is certainly enough -- that problems arise. The added torque compresses the bushings fully and very quickly under hard accerlation, changing the rear axle geometry on the move and making for some rather unpleasant handling traits.

Porsche was well aware of this potential problem and stiffened the rear suspension bushings of the most purposeful 993s, the Carrera RS and GT2, also known as 911 GT. Apart from homologation of these parts for competition, they also keep these very powerful cars pointing straight down the road no matter how much power you feed in -- and the difference in precision is staggering. Porsch engineers say that, if you stiffen up the lateral bushing enough to contain excessive movement, you can afford to make the spring and shock rates softer in the vertical plan to take the edge off short, sharp bumps. Of course, this is a Porsche problem that added power only accentuates and a CTR2 with the harder rear suspension bushings achieves near perfection.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Don't know if this helps. Good luck.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">John H, Is this aimed at me or Bob ?
If it is me, I have the stiffer GT2 bushings in all the linkages, it is just the front top mounts which are stock rubber.
{edit} I have just re-read and it is aimed at Bob.

viperbob

Thanks John, this could indeed be the problem. And TB993TT, since you have a lot of power and you have the stiffer bushings and are not experiencing these problems leads me further down the path that it may indeed to time for another upgrade.

Thanks guys!!!!!!!

SMB993TT

I have the RUF version of the PSS-9 suspension and was told by Andrew at Weissach that the RUF shock settings are opposite the Bilstein settings, i.e., the higher the number, the firmer the setting. According to Weissach, 9 is the firmest setting for the RUF PSS-9.

I am trying to confirm this point again with Weissach and will let you know if they come back with something different.

Steve