My Tweeks catalog (Cat. 30E, page 160) provides the following caution:

"If Bilstein shocks are used in conjunction with shorter aftermarket springs, the shocks should be Sport type. HD type shocks are not suitable."

This is the only catalog I have making that claim.
My guess is that the folks at Tweeks believe that Bilstein HD would already be partially compressed with shorter springs and thus would not provide the full range of travel before being fully compressed (bottoming out).

Some history. Several have recommended the H&R lowering springs with Bilsteins HD shocks at this forum. For example, Steve Weiner gave such a recommendation (along with RS adjustable sway bars) for a combination street/track set-up back in August. That recommendation was reinforced by several other knowledgeable rennlisters in a very recent thread.

My case (what I'm really interested in, of course). I have a street/DE/autox RSA which came with the M030 sport suspension standard, but those springs were replaced with H&R progressive lowering springs for the RSA (spring rates of 250-275 front and 270-295 rear). I kept the OE swaybars (after trying an adjustable front bar) and Boge HD shocks, which now have about 41k miles and 10 years on them.

Your advice please; keep the Boge HD, or replace with Bilstein HD, Bilstein Sport (I drive it on the street too remember), or wait for the PSS-9 system for the 964 to come out (so I've heard from one rennlister, but when will that be available?).

Thanks.

Jim

 

I think you'll find there is no such thing as a Bilstein sport for the 964. They sell the HD, as you noted. Jeff Curtis posted his discussion with Bilstein awhile ago, saying they didn't want to market a "sport" shock, so HD is the best descriptor you get on an improved street shock. Perhaps you're thinking of the various racing Bilsteins, which are also used on the European Carrera RS, as well as on the cup cars. Remember that the springs are going to have alot of influence about your ride. If you're comfortable as with what you currently have, adding a better shock like the Bilstein HD is going to provide more control, but shouldn't make it a bone jarring ride by itself. Jeff Curtis installed the Turbo H&R springs on his with the HD's, and has been pleased with them. (I have the Carrera RS suspension on mine). As far as the PSS-9 for the 964, I heard this week from someone who talked to ***** at FVD who said it would be another two months.

You can call Bilstein at either the East coast or West coast facility and talk to them. I've talked to the East coast people a few times, and once to one of their engineers in their West coast office, and found them willing to help with information and discussion on alternatives.

 

As a thought, why not see if through one of the RennList dealers of choice (numerous appear to like Gert), you could obtain the shocks, springs and front and rear anti rolls bars (five position front, three position rear) -- and the hardware (e.g., drop links, shock mounts, etc.) appertaining thereto -- of the Type 964 Carrera RS. And, if that set up is not racy enough, go for the springs and shocks of the Type 964 Cup Cars.

 

Instead of the mix and match approach of one part from one source and another part from another unrelated source, neither of which sources are coordinated nor have the engineering facilities nor the data base of the factory, why not go with factory designed and tested pieces

 

I just sent in an article with pictures discussing two 964 Carrera RS suspension installs, one on a 90 C2 and my 93 C2. The article will be on John Miles <a href="http://www.porsche964.co.uk" target="_blank">www.porsche964.co.uk</a> website in the near future. I went with the RS setup for the reasons Robert mentioned - all the parts go together.

 

And with factory set up suspension, should you be a serious racer, you might be able to install factory brakes far more serious than the "Big Reds"!

 

These brakes utilize 32 mm thick rotors front and rear and 24 mm thick pads (RS19 for endurance) -- and the special factory lightweight alloy bells (hats) -- and, of course, the factory centerlock system.

 

Thanks for your responses.

I'm not making any progress in my efforts to learn why Tweeks says the HD Bilsteins are are not suitable with shorter (lowering) springs. The woman I talked to when I called the Tweeks number didn't know, and Bilstein isn't open today. I'll call again next week.

No Bilstein Sport? My FVD-USA catalog lists the Bilsteins for my car as "Sport." Maybe they are the same as what others call HD. FVD also lists separate Bilstein applications for RS and CUP. The Tweeks catalog lists the Bilsteins as HD (with the warning not to use them with shorter springs), and the Performance Products catalog doesn't mention HD or Sport; -just "Bilstein Ultimate Performance Shocks", but I suspect they are HD.

The RS system is an attractive, but stiffer and more expensive, alternative to the H&R/Bilsteins.
I'd also like to know more about the PSS-9 for the 964 that's coming. I'm not sure I know enough to handle that much adjustability. Initially, I was just going to get new shocks. Although my car seems to be driving as well as ever, I know the shocks fade so gradually that it's hard to notice. Your responses are certainly in contrast to those of my mechanic ("What's wrong with what you've got?").

 

Jim - if I recall correctly, the Tweeks catalog refers to Bilstein "Sport" shocks in connection with models up to 1989, which I would take to mean pre-964's. It still makes no sense, mind you, but I think it makes this misleading terminology moot twice over, since (1) you have a 964 and (2) there is no such thing as a "Sport" Bilstein, as the others have said. I have the FVD-USA catalog as well and I'm guessing we're in the midst of some kind of strange semantics-related thing because the FVD catalog part numbers for the non-RS, non-Cup, "Sport" Bilsteins are exactly the same as the part numbers for Bilstein "HD" shocks in the Bilstein catalog. To answer your question, the Bilstein HD's can be used with H&R lowering springs. In my opinion, unless you know exactly what part you want, and you're 100% certain its the right part, about all you would want to buy from places like Tweeks is a keyring.

 

Steve Nugent

This is interesting. I contacted FVD in Germany a month back, to confirm the part numbers of the Bilsteins they do with the Eibach springs here (as I didn't want HD's). The part nos. actually corresponded to the Bilstein B6 Sport shocks, not the HD's.

Pretty strange?

Christer

 

MY suggestion would be to stick with your Boge M030 shocks and the H&R springs that you have...they work well together...don't think you'd find much difference in changing the shocks to Bilstein HD.

I have Bilstein HD shocks and H&R lowering/sport springs for a 965, stiffer than the ones for a 964...and they work great!

***So to answer your question, I have NO idea why Tweeks would claim that you shouldn't use shorter springs with the HD shocks...just ask the people that were in my run group with modified, even full race prepped Porsches this past weekend. ***

I would wait for the PSS9 to upgrade from what you have now...or, in my opinion, it's not worth the hassle.

I, for one, am awaiting the PSS9 kit for the 964...then my HD/H&Rs will be "FOR SALE"!