Michael Melton

Hello All, I've been searching for months now trying to gather information. While I have been successful finding bits here and there, I'm looking for someone who can help me get based on my plans. I'm going to list my mods below as a reference, but what I'm looking for is a Sway Bar diameter and spring rate suggestion for my specific application as I have not ordered those items yet and dealing with panhard bar location. While I understand I'll need to possibly fine tune, I just want to get as close as possible.

1986 Camaro z28 Iroc
if it makes a difference car has a 406sbc and built Gforce T5
Car is putting down about 490hp/505ftlbs @6400 on the dyno.
fronts wheel/tires 18x9 with 275/35/18s
rear wheel/tires 18×10.5 with 315/30/18s

front: umi tubular A arms with endlinks
umi camber caster plates
On car adjustable koni yellows
factory iroc sway bar
beltech 2" drop spindles
"GC weightjacks pending spring rate"

rear:
1998 trans-am NON WS6 rear end with 18mm rsb
On car adjustable koni yellow
founders performance double adjustable phb and adjustable phb relocation kit
Founders lca/lca relocation brackets/torque arm
"GC weightjacks
Car will be used for weekend driving, time trial racing, and hill climbing.

the drop spindles in theory should lower my CG and keep my RC relatively the same up front. In the rear I'd like to come down about 2" to match the front. This again should lower CG but will affect the RC in the rear. To combat this I have the phb relocation kit and adjustable phb. This is where I am unsure I should go with swaybar and spring rates. It is my understanding that I will need to stiffen up the rear spring rates and ideally run a 24mm bar. I haven't ordered any of those parts and would like some input before I do.

Thank you.

Lonnie P

Your drop spindles may put your tie rods into the wheels, depending on the backspace you are running.
You may be better off with stock spindles & an extended lower ball joint.

With a dropped panhard you will want more rear spring rate, but is also depends on the front rate you are running for balance.
Unfortunately a lot is driver preference as well as how far you drop the panhard, but I would think no less than 175 & more likely a minimum 200lb rear spring.
The more rear spring you run, the less bar you need. I run a 150 rear spring & 24mm bar.... the car handles very well, but if I lower the rear roll center, it under steers terribly.
I want to lower the roll center also, but have not experimented with springs yet. I was going to try a 200 or 225 as a starting point.

Michael Melton

Thanks sir. I appreciate you pointing out clarence issues. The car is assembled now and clearance is good. I stumbled on your older posts on the subject. It looks like im just going to order 900/175lb springs from ground control and keep the 18mm bar and phb lowered parallel with the diff. I'll just have to push the car until something gives and start changing one variable at a time.

soloc4

If you are interested, I have a set of Eibach 800lb springs that were intended for a setup exactly like what you have now. I sold everything except the front springs, so I will let them go cheap. They are new in boxes, never installed. I went in a different direction with my car. PM me if you’re interested.

TEDSgrad

iTrader: (4)

I think the #900 front is fine - that's what I have with drop spindles. Previously had 9" Eibach #850, but changed to 11" Hyperco #900 and saved #1 in weight savings.
If you already have new rear Koni's, then OK. New tech in rear coilovers is better option and eliminates the addtl. cost of rear WJ's. Detroit Speed is good to watch, but pricey. They offer #275 for the rear with no mention of rear RC drop. An instructor I had, told me he was going to run #300 rear with no bar. I was skeptical, but sure enough, the heavier spring in back is an improvement. I have RideTech's with #250 and axle side PHB lowering bracket only and 19mm bar with 12 bolt..
Detroit Speed





Stock 24mm vs 19mm

3rdGenA/SRacer

I have a very competitive SCCA American Sedan 3rd Gen. I dropped the rear bar and put more spring in the rear and the car was better. Curretly running 900 front and 275 rear.

//<86TA>\\

iTrader: (14)

250lb rear springs and a 19mm bar work well for me with a similar setup.