1st Gen F-Body spring rates

[XcYZ]

Hey guys, I was wondering what you're using for spring rates in an aggressive street setup. I currently have 175 lb/in leafs and I'm leaning towards 550 lb/in coilover, maybe even 600 lb/in now that I have the twins hanging on the motor. I'm curious as to what you guys have for spring rates and what you think of them. I've never had a 1st Gen that will be this stiff spring wise.

[Steve Chryssos]

Scott,
You should try to do it right. Start by measuring the eye to eye distance of your coil-overs with out springs installed at desired ride height. For example, my car is set at 13-7/8". Then you need to borrow or rent a set of corner scales (You might be able to get them directly from Intercomp). You really should know the weight at each front corner at ride height. Get that data and then you can best select the proper rate spring. There are other factors, but that's a good starting point.

I have a modified ARDF clip with QA-1 coil-overs so I cannot provide a fair comparison (different spring location, angle, probably different length and definitely different corner weights)

[parsonsj]

Scott,

I have an Excel spreadsheet from Katz that you can use to figure out some spring rates.

However, to use it, you need to know everything: vehicle weight, front/rear bias, spring angles, motion ratios, wheel travel, lateral G loadings, etc. etc.

On II Much, with a vehicle weight of 3100 lbs (est.), 48/52 f/r bias (also est.), nearly upright springs, motion ratios of .7 in front and 1.0 in the back, it recommends a 475 lb spring in front and 225 in the back for a street setting. For a race setting those become 550/250.

Those design parameters are with 2 inches of bump and 2 inches of rebound travel and allow 1.0G on the street setting and 1.15G on the track settings.

I'm happy to send it to you if you want to play around with it. Katz does good work.

jp

[XcYZ]

I used to have access to a set of digital scales, but my friend retired from racing and sold the setup.

John, I might just take you up on the offer of the spreadsheet. Sounds like a cool tool to mess with.

[parsonsj]

Done.

Check your email.

jp

[chicane]

Stock sub:
720# linear front, 320# 3-leaf custom rear.
3/4" front bar
No rear
Custom valved Stein's 350/150F; 275/110R

But.........with your wheel and tire package I would have to drop about 100# to compensate.

[Jay Hilliard]

Scott,

I have DSE's coilover setup and Kyle normally recommends #550, but I previously had #600 Hotchkis conventional springs before the conversion. Since I have cast iron heads on my motor, Kyle recommended to split the difference. #575 afco coilovers springs is what I ended up with.

my 2 cents,

Jay

[XcYZ]

Jay, have you scaled the car? What do you think of those spring rates?

What is the spring rate of the rears?

[Jay Hilliard]

Scott,

I have not scaled the car. I'm still in the rebuild mode. I felt the 600# springs were a little too stiff, but I didnt have nice shocks (koni, bilstein) to compliment the springs. I do plan to scale the car though.

I am running 175lb/in Hotchkis leafs in the rear.

Another thing I plan to do is actually test the spring and find out exactly what the rate is. I don't expect much of a difference between the two springs, but it would not shock me if the 575# spring actually rated 570 or 580.

However during my circle track racing days, afcos and hypercoils were closer to advertised rate and stayed there (no spring set).

I will let you know what I find when I get to that point and please do the same.

Jay