Springs or Valving???
 

So to paint a quick picture, I have a '95 FM2 turbo track toy, about 215whp. Currently running 15x9's with 225 rivals. Suspension is a set of fatcat coilovers with 700/325 spring rates, hollow front bar no rear bar. They are around 5 years old now, and the owner at the time they were made tracked Road Atlanta / VIR (I believe FCM factors in track conditions when you order, if not, disregard).

My current home track is a small countryclub style facility, Harris Hill Raceway, in Austin TX.

The track is far from "smooth as glass" and I seem to have major issues with the rear end becoming unsettled over some of the larger undulations. It wants to bounce / wander vs absorbing the bump/hump and settling back down, even in a straight line. So bad that I have to let off on the main straight. I'm a novice when it comes to working through suspension setups, so I'm looking for some opinions/advice. Does this sound like an issue from too stiff of a spring, or from improper damping? They may be getting due for a rebuild...? Any thoughts are welcome, if you want any more details let me know, thanks!

FWIW we have an NC on Ohlins and this same bump doesn't upset the car anywhere near as much.

What's your ride height? (pinch welds)

Edit: damping can be a factor for sure, but so can bottoming and/or droop travel. Those rates, with no rear sway bar is puzzling to me but it wouldn't necessarily create this issue... unless you were bottoming the car or running to low.

Don't have measurements off hand, it was setup and corner balanced a long time ago, but it is not too low, here's a photo for reference. I'm wondering if it is a lack of droop travel issue, I wish it was at home right now so that I could take some measurements. Stored at the track.

Edit: I need to take a look at everything on the car and see what the full setup is. NB tophats, etc... I bought it fully setup and it performed great at every track I ran in IL/WI, but down here with the rough track it clearly isn't ideal.

Looks too low for stock tophats to me. Take pictures of the bumpstops.

Lol, no. That's kinda high actually.

Are FCM Konis or Bilsteins? If Konis, they're junk. Get rid of them. If Bilsteins, it's possible they're blown, but with a good shock, your spring setup should be fine. You're definitely describing bad shocks.

Rough estimate, but we run our Lucky Dog enduro car about an inch lower with NB hats and have no unsettling issues. We also have MCS with internal bump stops, so that helps too.

If your shocks are blown, I bet you'd actually have better handling if you slammed it onto the bump stops*.

*Don't do this.

Yeah it sits pretty high IMO, higher than a miata on lowering springs, I'd know because there are about 40 of them parked at the track at all times.

The FCM's are Bilsteins, I'm thinking the rears might be toast. I'll pull them off the car if I get some time this weekend and get to the bottom of it. And if it doesn't have NB hats I'll upgrade.

The rear, with 325 rates and stock tophats just looks like it will bottom out. Ive got 350 rear rates and need ISC tophats at about the same height on the track with Hoosier takeoffs. Especially on a rough track like Sebring or ones with outside curbing at track out like Road Atlanta.

But, yes check for blown shock and take pictures

I'll bet they're blown and I would use a rear bar. The only time I've liked no rear bar was tighter ax courses because on anything other than very tight turns the rear lifts.

I'll have to source a stock bar and give it a try. To be honest I bought the car with this setup and never messed with it, thanks for the advice!

If you need your shocks rebuilt, Dave Whitner is local at: Whitener Racing Shocks
National Champion AutoX'er multiple years.

Thanks for the heads up, I just checked with him and he doesn't do rebuilds apparently. I have a few other recommendations from friends, hoping one can make it happen.

Shocks

I'd take the chance to upgrade to a better shock.

I considered upgrading my setup, but it's hard to justify the money for a weekend toy. I'm going to see if I can get some rebuild quotes and make my decision based on that.

Well looks like the local rate is around $120 a shock. I figure I get them refreshed, throw some ~400lb springs in the back, upgrade tophats if they are still OEM/NA and add a factory rear bar when I can track one down. Should be a nice improvement for the money.

Little update. Got out to measure the car, it has NB top hats and the pinch weld measurements are 4.6"front 4.8"rear.

Did you try looking at the bumpstops if they haven't crumbled into dust?

Yes, everything looks fine under the car. No leaks, and the FCM bumpstops are in great shape.

When the rear of the car settles after a speed bump, are both sides damped, or does the car go into some kind of diagonal corkscrew movement?

It doesn't remain perfectly straight, definitely requires some correction/steering input as it settles down. I had attributed that to the bump likely not being perfectly even, but if you have some other thoughts I'm all ears.