TTopJohn

107,000 mile 99 Z28, with all the factory suspension pieces still in place. Couple of chassis mods (SFCs, STB). Stock 16" wheels.

Let me start out by saying I am very happy with the way my car rides compared to every F-Body with a modified suspension that I have ridden in - the modded ones I've been were louder & harsher. Compared to them, my car feels like a Cadillac STS.
But while my aged factory setup is nice and comfy over larger undulations, it can jiggle the kidneys over broken pavement - sharp, sudden impacts are not it's forte.
And it could be a little sharper, a little more controled in quick side to side transitions.

I think there may be some room for improvement. And at the very least, I'm going to need to replace everything with new OEM stuff fairly soon with my mileage as it is.

Goals:
1) No increase in harshness or noise. This will not be tolerated. I'll replace OEM with OEM rather than make the car noisy or harsh.
2) A bit more ride control - I think that the kidney jiggling over sharp impacts is a result of under damping by the stock DeCarbons. Thinking that more damping would actually smooth out the ride.
3) Not much reduction in ride height - prefer no drop. I like stock ride height because it keeps the front end free of scrapes(I don't have one scrape on the nose in 107K miles) and it gives more suspension travel to work with.
4) Sharper handling in transitions - now, it handles great once it takes a set in a corner, but quick transitions from side to side can upset it slightly. Notice that this is last. I think the stock setup really handles great, you just have to be smooth with your inputs. So if I just keep handling capabiltiy the same, but increase comfort, that's fine with me.

Don't care about weight transfer for drag racing, won't be at the track. Car may see some road course lapping in a few years.

Basically, I'm shooting for BMW like, "grand touring" behavior from the suspension, with the caveat that it is a live axle so it will never like midcorner bumps.
Soft enough to soak up bumps, stiff enough to handle cornering.


Ideas:

1) Stock Springs, all new rubber bushings(don't want squeaks from poly), and Bilstiens (either SLP or revalved from a suspension specialist like LG or Strano, or someone).

2) SLP Level One setup -
all the car mags reported that Firehawks with this setup had a more compliant ride than stock F-Bodies, and handled better. They (C&D and High Performance Pontiac) said the progressive rate springs had an intial softness that was great for soaking up bumps, and then got stiffer to handle cornering - said they were great combined with the SLP valved Bilstiens.


3) ?


Am I correct in assuming the stock springs are fine for what I want and the shocks are what I need to focus on?

Also, I don't really see a need for LCAs, PHR, or a Torque Arm "upgrade" for my goals. They seem like ways to increase noise vibration and harshness, with not much benefit unless you are trying to improve your 60 foot times. Am I correct/incorrect?

I realize not many want an all purpose daily driver setup like this, but perhaps some of y'all have some input.

trackbird

iTrader: (4)

The SLP kit may be a good choice for you. Almost any shock you buy will be more aggressive than the stock shocks. Increasing rebound damping will tend to make the car feel like it rides more stiffly, but it also increases transitional handling performance (not alot, but it will change the way the car takes a "set" in corners, slightly). I suspect that your harshness over broken pavement is due to the suspension impacting the bump stops due to excessive travel. I slight increase in spring rate and compression damping may be beneficial without having too much impact on your ride quality. The key word is "slight" increase. Too much of a good thing is no longer good, and you sound like you are rather picky about the ride of your car (which is ok), just don't go too far. The SLP kit may do all of these things for you. Or, you may want to contact Sam Strano at www.stranoparts.com for shocks custom valved to your application. The other option is Koni DA's. You can then set the ride to be as stiff or soft as you'd like (to a point), but those don't come cheap either and border on overkill for your application (unless you want to part with lots of disposable income). I hope this helps!

Good luck!

TTopJohn

Thanks for the advice!

Interesting theory on the harshness over broken pavement - if I'm impacting the bump stops on sharp impacts, that would explain why the car is harsh there but fine on larger undulations that aren't as sudden. RR tracks are harsh, but speed humps on a neighborhood street are nice and smooth.

Looks like I'll be picking from Bilstiens (either SLP valved, or Strano custom valved) or Koni DAs

The Koni DAs - while they might be overkill for my needs right now, in a few years I do plan to get the car on a road course for the occasional lapping event / driving school. They could be worth it there.

The only thing that bothers me about the Konis is the chance of mucking up the ride/handling with all the adjustability. I know that rebound damping is how the shock lets the spring expand and compression damping is how the shock lets the spring compress, but I'm not quite sure how changes to each effect ride and handling. So I doubt I will be able to adjust a shock as well as a suspension specialist (like Sam Strano or Lou at LG). Kind of like on the Playstation - Gran Turismo - you buy the mega adjustable suspension for your car and it handles worse than stock because you can't quite set it up right.

And maybe a slight increase in spring rate. I know you can get custom valved shocks, but what about custom spring rates? Or am I stuck with off the shelf "lowering springs"?
What about the stock springs? Could they the best bet for my goals, or do I need something with a different (perhaps progressive) rate? You always hear that a setup with softer springs but stiffer shocks and swaybars will handle and ride better.

Sam Strano

iTrader: (41)

John,

You have options, however I truly think there is a simple answer to your situation. Either Koni SA's all around or our Koni/Bilstein (front/rear) combo.....

Here's why: The Koni's up front have a provision to run a second lower spring perch height. About 3/4" lower than stock, but allows you to use the stock spring, which means none of the things you get from stiffer springs like harder ride. Second, the damping can be setup anyway you want, from soft to brick stiff and easily changed until you find what you really like. Third, if you desire to run stiffer springs in the future, you have plenty of shock to damp them. Fourth, shocks are the weakest stock link in the entire suspension on these cars. Fifth, it's funny you said "Grand Touring" like ride, I very often explain the ride using stock springs with excellent dampers are very BMW M3-like. Not harsh, but firm with excellent control. Sixth, your complaint about the rear being harsh is because of the rear shock, but not because they are underdamped (though they are).

See, rear DeCarbon's don't like to compress over small bumps and they tend to overrule the soft spring in those situations making things jittery.... Then when you get the springs to compress, the shocks have an utter lack of rebound damping, causing the rear to bob, and move around much more than it should.

I do think you need better shocks. However, don't be afraid of having adjustments. If you do something you don't like, it's easy to go back. Shocks add stability to the platform and good ones work wonders....

All that said, as you know I do a lot of revalving of Bilsteins. I feel they are a bit soft in the HD form for anyone wanting good handling (that doesn't mean revalves will beat you up). Each revalve is done for each customer so there is no one size fits all. Honestly, the revalving on the front shocks is based on what I like about the Koni's damping. They are not copies, but similar barring the abilities to adjust damping and choose ride height.

SLP Bilstein's. I'm an SLP dealer. I use a lot of their stuff, and they treat me well. I can happily sell you an "SLP" Bilstein if that's what you want. BUT, IMHO I do a much better job at the shock valving than they do. SLP has one shock, meant for their level 1 lowering springs. They do increase the rebound damping, but by a flat rate across the board, and despite any other parts that may or maynot be on the car. I take all those thing into account, and change valvings accordingly whereas they just add X rebound across the board. Also SLP actually takes compression AWAY from what's not a very stiff shock to start with. This, to make a nice ride with the stiffer spring. However, with stock springs you actually get more movement, and more sudden movements because of there is less compression damping.

The reason the Level 1 has a more complaint ride is because the shocks work better, even with the slightly stiffer springs, which shows how important shocks can be to ride.

What you describe wanting your car to be is what I build my cars to be. Maximize grip by maximizing the ability of the suspension to not be upset by road imperfections. If you want to go further, we can add things like swaybars to lessen body roll and the loss of negative camber that comes along with it. That makes the most of the contact patch of the tires..... And we can go on from there, but I don't think you'd feel the need once you realize what dampers can do for you.

Quite simply, you would not believe the difference.

TTopJohn

Exactly what I'm looking for - nice to hear that a set of really top notch dampers along with the stock springs can do that.

I appreciate you giving such a detailed explanation.

When I'm ready to plunk down the $, I'll give you a call. I've got 1.5 more years of law school to get through before I can put any more money in the car.

jRaskell

iTrader: (1)

I followed Sam's advice and put the Koni's on my car and I'm very happy with the results. The ride and handling is a night & day difference, especially how much more solid the rear of the car feels now.

Sam Strano

iTrader: (41)

If I'm not mistaken, you should have gotten your swaybar??? I was wondering if you got it installed and what you think of it? Just curious. Sorry for the hi-jack.