ptuomov

I am happy to take a gamble with the FSD shocks now, but I am still far, far away from understanding this whole suspension issue.

Here's an example of an issue that I don't understand. The stock upper shock mounts are rubber. So they act like a rubber spring and possibly also as a damper. Suppose I replace the stock upper shock mounts with a jointed solid mount. Now, the springing is done by the spring and damping by the damper (the shock absorber). That to me figures is an advantage of keeping the system linear and predictable, because the progressivity caused by the rubber is eliminated. Now, suppose I then add the FSD shocks which allow the spring to work with high-frequency variations. Am I now introducing back some of the progressivity and unpredictability to the system? I think not because the rubber is probably acting as both a spring and a damper and the FSD shock is just acting as a damper. But I am not sure, because I really haven't studied how suspensions actually work and I am just kind of guessing.

tv

Oyvind - the BMW guy specifically mentioned testing 10 E46's - some equipped with PSS9's and saying he did not like them. I want very firm springs and a shock that can absorb/smooth out bumps w/o noise and jarring.


Tuomo - On a race car solid metal mounts may have a use but on a Luxury GT for street use I want rubber between the body and all suspension pieces. I don't want any noise, vibration, or hard metal sounds getting to me. I doubt the rubber bits are doing much suspension work. Do you want solid metal motor mounts??


I am no expert - just read a lot and have fairly good ability to understand mechanical things and some common sense. These FSD's seem like the deal.

Okv

The PSS9 Damptronic option for the Cayman is not an ordinary PSS9 shock as I understand it, as it is mangetic with electrical control to be able to function as a replacement for the PASM original coilovers, just stiffer.

But that does of course not rule out the possibility that the FSD is better.

Okv

Yes, and it deflects by a measurable amount when you put the weight back on the wheels.

I did not measure the stiffness because I assumed it would be far stiffer than the springs anyway.
The rubber can be modelled as a nonlinear spring (gets stiffer as it compresses) and some damping.
If there is significant motion in these mounts that can lead to problems because this spring system is acting in series with the shock and thus not directly controlled by the shock.
I still think the movement is too small to be significant, but really one should of course never assume anything, rather do objective measures and actually know what is going on.

Carl has solid ones for sale, he also has a picture of a rubber mount that failed.

Okv

When working with the man who made my BM5 there were some specifications that I had to find for him, and then he selected a standard (I suppose) shock and made modifications to make it fit.

The mods he did was to make lower mounts that fit the 928.
Especially the rear ones are difficult due to the configuration of the outer lower rear suspension pivot, where the shock is angled and has to fit perfectly or else the pin will not assemble correctly.

At first I did not understand much about what and why he wanted, but eventually we figured it out, and I learned during the process.

To choose a shock, one must know:

- Top mount type and dimensions
- Lower mount type and dimensions
- Length of shock, fully extended and fully compressed, possibly also a typical operating length
- Spring rate and supported sprung weight (To determine shock valve settings, i.e. stiffness)

Shocks for a 928 also must have spring perches (height adjustable), as they are coilover assemblies where the spring is mounted on to the shock.

ptuomov

I don't want solid metal motor mounts. I don't like noise, vibration, and harshness. Also, I don't like breaking the block mounting "ears" off. That's a solid no, pun intended.

(I would like to get very stiff rubber motor mounts, because my clutch is a piece of **** SPEC 3+ that doesn't work as a street clutch should. Stiffer mounts would compensate the POS clutch, I am hoping.)

I am naively thinking that making the upper shock mount solid would not cause that much NVH. After all, isn't the shock absorber damping the NVH? That's its purpose, right?

928 at last

Anyone?

Hilton

From the 928intl website:

ptuomov

I would feel better about those if they'd have a ball joint. (Not everyone agrees with me.)

ptuomov

Koni rep's response: "Nothing in fsd line that will fit. Sorry."

I don't have enough pull, that's clear. Someone else has to contact them via different channel. I don't know who to call.

Okv

The Koni FSD seems to be a non-configurable shock made for each car with one fixed setting.

To be able to fit the shock to a 928, it has to be configurable.
The valving must be configurable, that is easy to understand, but also the top and lower mount, as well as the length has to be configurable.

Shocks with such options are typically types intended for racing applications.

But, then you would not get the FSD?
Correct, but from the information on the web site it is just a modern technology shock, with properties that should be possible to get from other types or brands as well.
The great idea about them is what they call the frequency selective damping, which they state gives a controlled and stable handling and at the same time excellent comfort.

I do not think it is realistic that a new 2010 developed shock will be made to fit the 928, a car that went out of production 15 years ago and where the total production over 17 years was less than what Porsche makes of the 911 (==997..) now in one year.

ptuomov

If I've understood this correctly, the FSD system is just a fancy valving. The shock body itself shoudl be irrelevant. The FSD valve system I believe uses oil instead gas, so that's a difference relative to the usual 928 shocks. Other than that, I don't understand why they couldn't put the FSD valve system in an adjustable universal shock. That doesn't mean there's no reason, just that I don't understand why they couldn't do that.

In any case, the whole suspension plan is now firmly back on the drawing board. USPS refues to deliver my study materials from Amazon for some reason, let's see if I can figure out a way to get them for the holiday.

Cheburator

all shocks use oil, it just happens that some have inert gas sitting on top of them to prevent the oil from boiling. very rough explanation, i know, but you get my drift

tv

That is how I understand this FSD system also.

No practical reason why it can't be built/sold for 928's. As I said Koni alreadty builds and sells a 928 specific shock. A tube is a tube. Just switch the crap inside.

It would never get done by calls from customers. It needs our vendors to make the calls. And why wouldn't they. This could transform 928 handling and make owners very happy, give the car new life.................

High performance shocks and upgrading to them is a niche business and more likely to be done by older cars with a strong following like the 928, so I don't buy the volume argument. And who on this board would not upgrade to these if they are as good as claimed even if they had just installed others.

Call it the Koni HP

76FJ55

Sound to me to basicly be an inertial valved shock. I think similar tech has been used in the mountain bike, motorcycle and auto industry for some time. Edelbrock even has an offering, in their IAS shock