CloseI just posted this in the TT section, since it was initially prompted by an excellent series of posts by member Cannga. But it seems germane to your question, so I am re-posting it here. (And since my car is a 997S, it rightfully belongs here regardless)...
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Sorry for the delayed response, but have been on some biz travel. Finally got a chance to catch up. First things first:
I now proclaim the suspension upgrade for my C2S (Cab) complete. I've taken a minimalist approach (for now) going only with Damptronics and sway (H&R) bars. By the way, I don't know whether it's because I chose H&R (versus GMG) or it's an 'S' and not a 'TT', but the bars I received had no adjustments in the front, and only three settings in the rear. In some respects, it simplifies life in that there are fewer setting combinatorics to play with, but I would have wanted more adjustment options. I've tried to follow Cannga's guidance to the letter, with the coilovers, stiffest sway bar setting in the rear (nothing to adjust in the front) and a GT3-like alignment. This was the last step so a few added comments re this phase. On my 'S', I was only able to squeeze about -1.0 degree of camber our of the hardware. I did not choose to upgrade the shock tower components to give me more adjustability so that's about it for now. And for an early poster, it is certainly not true that the alignment provides 75% of the value of these changes. Just the other way around. The new coilovers are 'the thing', the bars likely have some value (I could not do the before/after experiment here), and the alignment certainly helps in improving with turn-in (or dynamic instability if you're in to another line of machinery), but nothing breathtaking.
So, my findings are much like Cannga's. This basic mod is a must-have. I do not know what incremental value new drop links, et al would provide though I suspect it's diminshing returns. And this is not a track car. Just an aggressive driver. Further, although the ride is a bit firmer, I don't think that this aspect should sway (sorry, bad pun) anyone from going with it. The ride is just fine, immerses the driver in the experience, does create more road noise - especially tire noise - likely for the reason Cannga cites, and the handling is night and day. Now that I've been driving it a bit, I do wish the Damptronics had some manual adjustments. Though I have no formal experience in this aspect of car mods, it feels like it could use yet more rebound damping to expunge the last of the P-car nose bob. It's mostly gone, but not thoroughly. So, for those who are still considering the change, and they want to get it 'just right', and are willing to defeat their PASM system, Moton's or alternative Bilstein's, Penske's, etc., might be the way to go. OTOH, I have no first-hand knowledge re the ride quality trade-off with these others, so caveat emptor.
Finally, I had a bit of
a grin on my face when the fellow doing the alignment (at TCDesign -
very nice folks) measured and found that, after lowering the car front and back 18 MM, I got the ride height corner variance to +/-
1.5 mm. He said that it was near impossible to do - and totally
unnecessary for a street car! :) So I guess the techniques cited on my
blog (http://autopianviews.blogspot.com/) worked. Not a true corner balance by any means, but sufficient for street use. I chose not to drop the car the full 20 MM as discussed on another thread because of road object risks and my plan to substitute the GT3 bumper for the current stock one. Not having the comparison in lip heights, I am not sure yet what to expect. We shall see..
I have H&R lowering springs on my C4S. 30mm lower in the front and 25mm lower in the rear. PASM Normal is still comfortable, while PASM Sport is very firm and hard. I found that the handling overall improved after installing the springs and the car looks much better when sitting a bit lower.
05 Boxster S, Arctic Silver, H&R, PSE, FVD Stage 1
08 Carrera 4S, Guards Red, H&R, PSE
Feb 19, 2009 12:37:51 AM
I have heard of premature shock failure when PASM cars are equipped with lowering springs.
I wish that we in NA could order our 911s without PASM so that we could easily modify our suspension without these worries.
The problem with lowering spring is more than just about shock failure. It is that you are still stuck with the stock shock absorber, which, in case of the 997 Gen I with PASM, is a bad thing. The stock PASM's FIRM SETTING is way too firm and is of no use in my experience. It causes an unrelentingly stiff ride and actually is harmful to traction at limits.
For a "little" more money, the Bilstein is a much better option than lowering spring in my opinion. You now have new spring PLUS new shock absorber. The Bilstein shock absorber is technically superior and Bilstein PASM FIRM setting is night and day better and more useable than stock PASM FIRM, at least for the Turbo.
Regards,
Can
997 Turbo + Bilstein PSS10 (Review) + Cargraphic Exhaust (Heavenly Race Car Noise 
Review)
I'm a disciple of that which Cannga advocates. The cost difference is relatively modest. Both require removal of the OEM coilovers (and the spring-only requires incremental labor for disassembly for re-springing) and thus the labor costs wash. The Bilstein's are PASM compatible. Pretty much the only ones that are. So no 'faults' on the dash and the push-button ride settings work as well. The difference is night and day and, though I have not driven a car with OEM shocks and lowered springs, I can't believe that the fundamental OEM limitatations can be addressed by new springs alone.
Re the ride quality, it is firmer, but still quite acceptable. You feel more of the road/bumps/et al, but the car takes them in a more solid and reassuring feel. I would only caution that if you consider the stock car, in PASM 'soft' to be barely acceptable re comfort, than don't do it. But the ride change is really modest, the performance is spectacular, and unlike the stock coilovers, the PASM 'firm' setting is quite useful. And re-reading your original post, the standard PASM setting with the Billstein's is nothing near the misery of the firm setting with the OEM shocks. In fact, the firm setting with the Billstein's is also more comfortable than the OEM firm. That setting is just horrible, useless and I suspect damaging. At least to a convertible. I always felt like the pounding to the Cab chassis in PASM/OEM/firm was putting the car at risk.
To me, this is a 'must do' mod. On the list of performance-oriented mods (to say nothing of the car looking better when lowered), it is #1.
secondc4s:
Cannga, I assume that is a coilover solution? Does that shock work with the PASM? How does the "soft" ride compare with the original?
--
997 C4S - PSE; GT Seats; white side markers; red tail lights
Yes, it is the coilover I am talking about. The Bilstein Damptronic model is fully integrated with PASM (Bilstein is the OEM manufacturer for 911.). As far as stiffness comparison, Verde actually could give you a better evaluation because my experience is with the Turbo, not the C4S.
For the Turbo, using a scale of 1-10 for stiffness, if STOCK NORMAL is 1 and STOCK FIRM is 10, then BILSTEIN NORMAL is 6, and BILSTEIN FIRM about 8. But a numerical value doesn't fully describe how much more useful the BILSTEIN FIRM setting is. Some tuner has used the word "creamy" to describe the Bilstein Firm setting (as opposed to "harsh"), and I sort of agree w/ him. The difference comes not from the spring, but the superior shock absorber.
And I agree with Verde, the only time that I wouldn't recommend Bilstein is if the *STOCK NORMAL* settting is already at the upper limit of tolerable stiffness for you.
Regards,
Can
997 Turbo + Bilstein PSS10 (Review) + Cargraphic Exhaust (Heavenly Race Car Noise Review)
Thanks for the replies. Not sure how to describe what I like or dont like about stock. I am OK with standard on stock, but still feel the car doesnt "take" bumps but "hits them". Regardless of setting I dont like the way it takes bumps. Really like the expression "creamy"...
Last (?) question: how is the firmness related to ride height? Are they directly coupled or (somewhat) independent?
Is there a simple way to try? Is the ride comparable with that of the GT2?
secondc4s:
Thanks for the replies. Not sure how to describe what I like or dont like about stock. I am OK with standard on stock, but still feel the car doesnt "take" bumps but "hits them". Regardless of setting I dont like the way it takes bumps. Really like the expression "creamy"...
Last (?) question: how is the firmness related to ride height? Are they directly coupled or (somewhat) independent?
Is there a simple way to try? Is the ride comparable with that of the GT2?
--
997 C4S - PSE; GT Seats; white side markers; red tail lights
Firmness versus ride height for Bilstein: If you stay in the middle of the recommended range (approx. 10mm to 25mm lowering), there should not be much change in firmness.
If you lower the car too much, you risk hitting the internal bump stop -- bad. Conversely, if you don't lower it to the specified range (i.e. keep car too high), I've been told the risk is coil binding, resulting in car being too stiff.
Not sure if I fully understand you regarding the bump, but for the record, I should say that I have no problem with PASM Normal in the C2S. I think it's very well set up for a daily driver. But this is just a matter of personal preference; certainly YMMV.
Just a question though, what are your tire pressures? Are you at "Partial Load" setting with TPMS differential reading all zero? In my Turbo, I could easily and readily feel a 1 PSI increase and I think this is an issue that's neglected too often in suspension evaluation. The tire pressures must be set within recommended range or all bets are off. (For the audiophiles among us: This is like the stylus of the turntable. Most critical component and determines how the system sounds. But I digressed. 
)
Test drive? Unfortunately, for what I consider to be a true test drive (extended driving at, er.. a "decent" speed, hopefully over a few days), I think it's not going to be easy. OTOH, you are close to Sharwerks (Alex Ross, who posts here), one of the most trusted names in the Porsche community in California. Might want to give him a call.
Versus GT2? I drove the GT2 but unfortunately at the time my Turbo was not fit with Bilstein yet so I did not have a direct comparison. Based on what I know of spring rates and my memory, I would say the Bilstein NORMAL setting is a tad softer than GT2 NORMAL. And again, even in the mighty GT2, I find the stock FIRM setting to be jittery and too stiff and have little doubt that it could be improved upon. It would not surprise if someone were to tell me the best time for the GT2 at the ring was achieved with the Normal setting. IMO, PASM FIRM the first generation is a useless setting across all 911's and should have never been released. Just my 2 cents and I wonder if anyone at Stuttgart agrees. 
Regards,
Can
997 Turbo + Bilstein PSS10 (Review) + Cargraphic Exhaust (Heavenly Race Car Noise Review)
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