Originally Posted by
MJM Distributing
There is a lot of misinformation in this thread on this topic. I personally have had cocktails with an engineer at KONI at SEMA and spoke with him at length about this. Fact is, the FSDs are *NOT* valved to run with a spring with a spring rate any more aggressive than that of an Eibach Pro-Kit Spring, hence the reason KONI offers a kit (the KONI FSD/Eibach Kit) that utilizes Pro-Kit, not Sportline, Springs. Will the Sportlines "work" with the FSDs? Sure, they'll "work" and your car won't explode or anything like that, but they're engineered (i.e. valved) to work with the spring rates and lowering levels of Eibach's more mildly rated spring (the Pro-Kit Springs) and when used with any other spring not approved by KONI, you might not get the same dampening characteristics and/or ride quality as you would otherwise.
An interesting note on the subject of the KONI FSDs is that when asked why KONI chose Eibach Springs to mate with FSDs over all the other springs out there to choose from (KONI has relationships with Vogtland, as KONI Coilovers use Vogtland Springs and with H&R, as H&R uses some KONI Dampers in some of their kits), I was told that out of all the spring manufacturers KONI tested, that Eibach was the most accurate out of all of them in their lowering estimations. Meaning, when Eibach states "a 1.6 inch drop", then it was darn near the centimeter to being a 1.6 inch drop. I know many of us have installed springs over the years and said "Man, that's not as low as I thought it would be!" or "Man, that's a little lower than they told me it would be!" Well, according to the engineers at KONI who tested many different springs, Eibach's numbers are typically right on the money.
Feel free to PM me with any questions about KONI or Eibach products. As a Warehouse Distributor for both here in Texas, we always have great deals on either line not seen on our site for E46Fanatic members, including both our Group Buy on Eibach Springs right now and our "Buy Back" program with KONI Shocks and Coilovers where we buy back your old worn and torn shocks (in any condition) with purchase of any KONI Suspension product.