picking shock valving for handling

[jerome]

I am ready to choose which shocks I want to use, and after reading alot of technical stuff that I sort of understand, I still don't know what valving we want for handling applications.

I have a 82 S10, mostly street, but may see some autocross/road course when it's done. Looking for front shock advice here. 600# front springs, small bar. general info appreciated, but also need specifically which of these two is better. or are neither of them good?

These are both street stock shocks, monotube digressive valved Bilsteins.

Bilstein 213AK3050F
8.45" compressed/13.36" extended
131# / 206# digressive
3 / 5

Bilstein 213AK4040F
8.45" compressed/13.36" extended
197# / 154# digressive
4 / 4

rebound / compression

Thanks,
Jerome

[jerome]

I've been doing a little more research, and I've decided that I want to go with a different setup. I was planning on the stock shock location as seen above, but now, I want to move the lower mount out to the ball joint and have the shock go up through the upper a-arm to an upper mount built up from the frame with tubing. This is so I have more shock choices, more damping control, and I can use a weight jacker bolt for the springs. Since there is more motion when it is closer to the balljoint, I will probably be stepping up to a 7" stroke shock.

Questions:
Probably going to use these shocks:
http://www.speedwaymotors.com/p/5512,149_Bilstein-Steel-Small-Body-Race-Shocks-With-Ends.html

https://static1.pt-content.com/images/noimg.gif


As you can see, one end has poly and one has a rod end. Will this rattle my teeth out for daily street use? Anybody have experience with shocks that have poly and a rod end.

I still need to decide the valving, but now the choices are wide open. Almost any rebound/compression combo I could dream of. Where do I start? I really have no idea what valving to choose, read alot of books and they explain rebound and compression but have no recommendations on what works for a serious handling street car that will see occasional track time.

Thanks,
Jerome

[rattus]

A quick and dirty (horribly over-simplified) estimate can be calculated using some percentage of critical damping:

crit damp = 2*sqrt(k*m)

where k = spring rate, and m = unsprung mass

For AK series shocks Bilstein gives valving in terms of lbs - sec / 10 in, so you need to divide the valving numbers by 10 to get them into damping units, i.e. lbs-sec/in.

[Norm Peterson]

I think the motion ratios of both the spring and damper figure in to that equation, as the natural frequency you're looking at is the ride frequency at that corner. The mass term is fixed, but the stiffness term is the wheel rate. The spring MR would be squared, but I think the damper MR (which could be different) would only be a MR^1 function.

Those forces don't mean much without knowing the shock piston velocities that produced them, and even with the velocities the doesn't mean a whole lot more. It's a matter of how they get there.

Still greatly over-simplified, but you need to look at the shock curves, not just peak values (which are only single data points on the curves). Handling-related chassis motions are typically low shock-piston-speed events and for a performance road car you probably want at least 45% critical damping in that range. Bump responses, on the other hand, are relatively high shock-piston-speed events, for which you want much less damping (perhaps as low as in the ~20% range?). What's probably best is digressive shock valving, or force vs shock piston velocity curves that start off relatively steeply and flatten out once the velocity goes beyond some point.


Norm

[Marcus SC&C]

The thing is you don`t have enough data to do meaningful calculations with or any base line to go off of with the shocks in the new location. Even the best race teams WITH that information as well as logs of data from previous seasons etc. still change shock valving often. What you need is a set of adj. shocks with a wide range and the time and place to test and tune until the truck works the way you want it to. Then you can have the shocks dynoed to get your numbers. Of course at that point you`ve already achieved your goals so it doesn`t really matter what the numbers are... :) Mark SC&C

[Norm Peterson]

Here's a couple of links to some shock plots. Understand that there is some advertising content/slant to the text. Understand also that you can't apply the curves given to other car makes/models - I've only posted them to illustrate that you need to work from curves, not a pair of data points.

http://www.koni-na.com/presentations/mustang/

http://www.koni-na.com/presentations/civic/


Norm

[jerome]

Norm, I see what you are saying about the plots. I am far, far away from having any data necessary to make an calculated decision on shock valving. As it is now, the truck is an empty frame on wood blocks sitting on my garage floor.

I guess nobody would be able to say, "Oh, that sounds like you need 4compression & 4rebound." Does anybody know how much different valves are for shocks and how hard they are to replace? with a monotube shock like a bilstein will you lose gas pressure when you rebuild it with a different valve? I'm just wanting to know how easy it is to put in a different valve set to try.

Thanks,
Jerome

[Norm Peterson]

An engineer at Bilstein could perhaps make such a recommendation, although I suspect that you'd be advised to experiment either way from such a recommended starting point. Not all nominally identical vehicles are ever quite the same even before you get into suspension and wheel/tire package mods, nor do all drivers have the same handling "feel" preferences.

Here's some stuff about shock disassembly/reassembly and valving:

http://www.penskeshocks.co.uk/downloads/7000SeriesTechManual.pdf


Norm