BC

Did you explain that these shocks were not broken in as some say is suggested with new konis - to have them at half hard for a while? ( no source on this)

GUMBALL

Bill:

That was the first step. Now you know EXACTLY what you have on the car.

From listening to your explanation of the handling, I had a feeling that one shock might be soft. I had the same thing happen on a customer's race car - one shock's valving did not match the others.

So, NOW you know which direction to take as the next step in your setup.
The dyno is always a learning experience.

Bill Ball

These are internal Konis. Supposedly same valving as external.

Brendan, at this point I'm collecting information and trying things. Konis work FINE on George's car (stock springs) and do well on Tim & Cheryl's white GTS (?which springs) and Marc Thomas's GTS with stock springs. Now, these are not track cars.

I got these Konis directly from Koni via RMA - they are not rebuilt as far as I can tell. I'm aware of Hypercoils, if that is the 600/400 you mention. Hypercoils come in all kinds of ratings. I can't see how one Koni could accomodate the wide range of spring rates offered in various Hypercoil kits.

Maybe we can generate a good argument here. Maybe Koni quality has gone downhill. All I can tell you so far is the original set of Konis I got 3 years ago were essentially junk right out of the box and within 3 years they couldn't dampen a dishrag. The new ones seem better in that regard but still not adequate.

BC

While Bilsteins are as stiff as... well an old man on three blue pills.

Bill Ball

Louie encapsulated it. With a linear dyno chart you get too little damping in slow speed shock movement and too much in high speed. The shock guy said this is common for a standard street car shock - soft daily ride but not great handling when pushed hard. The front shocks exhibited this more than the rear. The rear had a more rapid rise in damping in the slow area (refered to as a nose), tapering off at the top. However, he showed me charts of other shocks and the curves were vastly different - some were essentially flat after ramping up early in the shock speed curve. I didn't absorb it all. I plan on spending more time trying to understand this better and go back with some other sets and talk to him more. BTW, this is not an expensive procedure: $85 for all 4 shocks and springs. He tests them at current setting, full hard and full soft. He did a few more settings when he saw the limited range.

Also, it's not like he's against Konis. He had tons of them in the shop and knows the Koni technical people very well. It's just that after his first experience with Konis idea of 928 shock valving, he's not too sure what they were trying to do. He thinks they made an average street shock. I dunno. With George's car handling so well, we need to get his shocks and springs on the dyno. I will pay for it and do all the labor.

Bill Ball

Here are the charts. Note that the full hard setting is not recommeneded even though the low speed curves look better. Note the linear rebound of the front shocks regardless of setting. He said that was good for braking - we don't brake in open road racing except at the end.

Comments?

worf928

True. Supposedly the same shock. However, the externally adjustables are converted in Koni's "race shop" - or so am I told. It would be interesting to know if the "race shop's" QC is better.

Bill Ball

It is true that all the other guys I mentioned as having good handling with konis are external...hmmmm.

worf928

And thus why I asked.

pmotts

I just installed Koni ext adjustables w/ Eibachs and gave them a good workout at our recent track event. I loved them but the only experience I have had is with stock (old) suspensions. I am having breakfast with Louie this week end and maybe he can take my Shark for a spin to give his judgment of them. I have yet to get the ride height right or get it corner balanced so there is still room for improvement.

Richard S

Bill, sign up for the Diablo Region trackday on Oct 5 at Thunderhill. Dennis will instruct, both of you can evaluate your setup on the track.

Rich

BC

Well, I may just have to get my externals revalved properly then for the weight of the car (less) and the springs (more)

SharkSkin

Bill, it sounds like exactly what you described... something about wallowing like a land yacht. So, it was under-damped, not under-sprung. Most land yachts are under-damped. Maybe Kibort's test was performed on a car with gas charged shocks vs your car? That would account for the different amount of sag.

As for the curve flattening out, maybe this will help. Years ago, I found myself dealing with motorcycle shocks that had progressive damping. the way it was described to me, the piston had orifices in it, some of which had(essentially) a little flat spring sitting just above the orifice kind of like a reed valve. When the piston(and fluid) was moving relatively slowly, the spring stood clear of the orifice. At higher piston velocities, where the fluid had to pass the spring to get to the orifice, the spring would move down and at some point it would close off the orifice, and flow would occur only through the remaining orifices around the piston.

This type of setup would give you the flattened curve you speak of; you'd get more and more resistance until you reached a velocity at which the orifice was closed, and beyond that point you would get the same resistance regardless of velocity.

The Koni seems to be behaving as if, with increasing velocity it closes off smaller and smaller ports. This would explain the smaller changes in damping at the higher velocities; less change per port closed off.

Maybe that will help understand what you're seeing on the charts, but it won't help solve the problem. The guy you talked to at Infineon has a better feel for this than any of us bench racers IMHO; If his impression is that you're under-damped for the spring rate then I'd say take his word for it.

Now, with these charts in hand, and with the knowledge that it *doesn't* work, you can start asking for data about other shocks and ruling out other shocks that may have similar curves. If you go with adjustables, you would obviously want something that starts off at the red/purple line on full soft and has room to go a lot stiffer. Ideal would be a setup that allows compression & rebound to be set independently, but I have no idea what that might cost.

Porsche certainly spent a fair stack of pennies figuring out their shock profiles -- since most aftermarket shocks are probably designed with the stock springs in mind, you might be better off just getting the same shock that Porsche provided with the sport springs. Unless, of course, you want to go with much higher-end shocks that are fully adjustable. Even if all you could get was a set of dyno charts for the sport shocks, it would give you a starting point for compression/rebound relationships.

Dennis K

Very cool Bill!! Did you end up going to Stasis Engineering?

I think what you're looking for is "digressive" valving, which is typical of racing dampers. There's a distinct knee in the rebound damping curve at a certain piston velocity. Street dampers typically have progressive valving.

I'm not sure if these Konis (either internal or external adjustable) can be revalved to fit a digressive damping curve. I think they're modded 8240 dampers.

Also, I'd be more than willing to have my shocks dynoed just to see what the curve is on these modded Bilsteins.

Bill Ball

Dave:

You say a lot of sage things there. I think you are right about the original suspension. The general behavior of the Boge red gas shocks and the sport springs was very good out of the factory. They were just starting to lose in some areas when I changed them out at 95K miles and 15 years, but overall were very competent. If nothing gets any clearer soon about what exactly I should do, that's probably the way to go. I'm very tired of fighting with these Konis. The shock performance shop I was at today can make them perfectly right for me, including double external adjustments with correct valving for the springs...at a pretty huge cost. Even the custom valving alone was going to cost too much. He said I should just start with a better shock rather than trying to fix these.