Coil-Over Shocks IRS C4 -> opinions please !

[Novette_71]

(just recognized this is the wrong place how do i move it to chassis? sorry.)

guys,

please help me.

i am getting frustrated with making phone calls around the world figuring out what to do with my coil overs.

i have 1 1971 chevy nova, estimated 1650 pounds on the front, 1450 on the back.

i have the wayne due C4 IRS setup front and rear.

front : ball joint to subframe 12.8", shock to subframe 10.24 ", shock angled 20°.

rear : ball joint to subframe 18.3", shock to subframe 11.2 ", shock angled 26°.

I wanted to use the QA1 double adjustable coil overs, but just heard from someone else QA1 is crap except for drag racing. can anyone confirm this or has good experiences with their products ?

my ride needs to be firm, but not harsh, should be able to do some good autocross, from seeing badpenny perform i would say that looks right for me.

from my feeling i would say i want 500# springs front and whatever fits to that in the rear .... when i tried these (a/b)^2 formulas the numbers where all non-sense dont know where i screwed up.

i have a 1994 viper with a paxton and a K&W stage III coil-overs and that set-up is pretty nice , maybe slightly less firm. maybe this helps someone for comparison.

if qa1 is crap, what would you recommend as a great product ?

thanks for your help.

[Novette_71]

so after browsing thru many many cars here in the forum i recognized many ppl have the qa1s so they cannot be that bad. i ordered the double adjustable shocks as well now.

i did some more calcs and ordered several spring sets.

now the only question remaining is : the viper has 515# front and 800# rear, so higher rate in the back.

on my car : i figured out the rear weight is less but the lever ratio is much worse so i almost came up with the same spring rate for the IRS.

anyone having the wayne due setup and having info about his setup with rates ? anyone who can confirm the rear sping rate might be even higher than the IFS value ?

[mfain]

I designed my own suspension for my 56 Corvette road race car, but it is based primarily on C-4 components/geometry with coil-overs. The following is my opinion after going through the drill (4 different suspension configurations). First, you need to balance the roll resistance front to rear. Two primary factors are the roll force (simplified -- the weight at a given end of the car times the lateral g applied at the center of gravity at that end of the car) and the moment center at each end of the car. If you left the geometry on your suspension the same as it was in a C4, then you can compare your car to the C4 and make an estimate on the spring rate differences. Your car has a higher front weight percentage than a C4, and the center of mass is probably a little higher. This would imply a need for a higher front spring rate than a stock C4 if you used the same rear spring rate. You may have noticed that newer Vettes (and the Viper) have gone to much higher spring rates in the rear. This is becaused they lowered the rear moment center, requiring a higher spring rate to produce the same roll resistance. This makes the rear tires do more work with a side benefit of reducing rear camber gain which keeps the wide rear tires flatter on the ground during acceleration. You might also have noticed that the Sprint Cup guys put on an outboard track bar adjuster that allows them to really lower the outer end of the bar -- this lowers the roll center on a straight axle rear end set-up and allows them to adjust the rear roll resistance in a hurry. If you changed any of the C4 stock geometry (track width, height of the suspension pick-up points, etc) then your best bet is to spend about a hundred bucks on one of the basic suspension geometry computer programs, enter your car's data, and let the computer due the calculations (moment center, roll resistance, bump steer, etc). Grassroots Motorsports Magazine has several programs listed. Once you get in the ball park, you can fine tune with front and rear roll bar sizes -- the bars also contribute to roll resistance.

I know this got a little complicated. That's why I recommend a computer program. As far as shocks go, I used AFCO coilovers for the initial set-up because they were fairly inexpensive and can be modified easily. Once I get where I need to be, I will switch to Penske or Ohlins shocks. You might want to contact one of the Corvette race suppliers (Guldstrand) for recommendations on your spring rates.

Good Luck

Pappy

[Novette_71]

thank you for your answer. seems like you put alot of brain power into this.

i ordered the qa1 and 4 sets of springs. since my geometry is 100% c4 front and 80% rear i go with the try and error attempt now.

i keep u informed and i really love your setup, esp. the rear pic looks awesome !

[ProdigyCustoms]

Project Prodigy uses a modified Wayne Due front stub. We run OA1 double adjustables and run 550s with a aluminum big block

[Novette_71]

thanks for the info i ordered 400, 450 and 500s

small block cast iron but aluminum heads, and generally the BB parts are heavier. plus i have no heating , no a/c, no wipers, no inner fenders (at least none from steel), no horn, so the variety i have chosen should be ok.

i start with the 500 and see how it feels.

parts come friday so some more waiting .....