A question for the leaf spring gurus

[KillerWolf]

Hey guys,

I have a 71 cuda that I'm setting up for a multi purpose car (aren't we all). I'll run mostly street, moderate drag (6x year) & the very rare open track at Road America. I would like to eventually run in the "One Lap" & "Silver State" events as well. I built a very serious turbo small block (800+ tq) & my main concern is getting that power to the ground at the strip, but I also want the car to ride & handle very well. I figure at any road course type events, I'll dial the boost way down to make the car manageable. I do not know the actual race weight, but with what I'm adding & subtracting, it should come out around stock (3450# curb) & close to 50/50 dist.
Here's my rear suspension plan. Your input would be greatly appreciated.

1. Hyperco 175-200# composite leafs w/ del-a-lums front & rubber rear w/ sliders. I've made, but not yet installed, inboard spring mounting, frame rails/connectors (3"x4" tubing necked down to 1-1/2" x4")
I plan on canting the springs (fronts in) for better roll stiffness & lateral support. The frame rails are angled stock at approx 4* inward. Is that too much offset (I've seen 2* used) & what harm would be done having that angle? What angle would you suggest (due to design, I'd like to keep the springs canted)

2. Caltracs, to be able to hook 800-1000 hp. That being said, I will be launching the car on mostly motor (2800 stall) & letting the turbo build against the gear (9" w/ 3.30-3.50 & A518 w/ 2.47 1st). I figure this will run well into the 9's & would like a 1.4 or so 60'

3. I was not intending on using a panhard or watts due to the canting & the fact that I won't be throwing it around through corners at ridiculous speeds. Does that sound feasible?

I've seen several posts with "chicane67"s custom leafs (built in "traction bar") & like the idea. Do you believe that those custom designs could handle the type of tq I'll be laying down & still have decent ride/road following capacity? Do you believe that my design in good for what I am trying to accomplish? & lastly, What would be the max angle I can move the front eye without problems?
Thank you very much in advance. I know it's a lot to ask, I just wanted to ask someone that knows.

Thanks,
Scott

[KillerWolf]

Chicane, pozzi........anyone?

[KillerWolf]

Anyone??

[Bryce]

typically i have seen the front eye 1" inboard compared to the rear shackle. Chrysler was able to angle their springs not sure what degree but it gave very good lateral stability where no swaybar was needed. This is what i heard recently from a chrysler engineer from the 60's.

[KillerWolf]

Thanks Falcon, I finally found the stock offset to be 1.67*, so I think that 2* should work well.
I'd still like to hear from Chicane67 on his custom leafs.

[Bryce]

from what i have read chicane used a traction device on the spring, basically just wrapping the second leaf around the eye as well as the first. its a good idea for stiffening the front of the spring and maintain some flex of the spring. i have not read anything about the anlge of the springs.

[Skip Fix]

Mopar had soem "Super Stock" rear leaf springs that hooked really good at the drag strip. Front half biased to rpevent wrap up. Not sure how they would do handling.

[High Plains Mopars]

Mopar springs from the factory already have a shorter front segment than rear segment to create a stiffer, less flexible front segment to plant power under accelleration but also allow spring movement during cruising with the longer, more flexibel rear segment. By comparison, many Chevy and Ford springs were more equal length and have greater tendancy to wrap up under accelleration than a mopar spring. To make the front segment even firmer and plant better, mopar came out with the super stock spring which has a front segment 2" shorter than the already short front segment found on your Cuda. What cal-tracs do is create a pivot point mechanism in the front eye that will rotate into the spring and effectively shorten the front segment by 2", thus duplicating the effect of a SS spring pack without the corresponding ride height change or ride harshness. SS springs tend to be pretty thick. If you look closely at a mopar spring, you'll also notice that the second leaf comes right up to under the spring eye so that the forward segement is adequetly supported.

Since they typically raise the ride height 2-4 inches, SS springs aren't the greatest handling set up. Since they are a monoleaf design with no cross support, I would tend to think Cla-tracs aren't the greatest either, but I will admit I have done no research nor have any first hand experience with them.

Mopar also makes their oval track springs which have the shorter front segment, like a SS springs, but are built in zero to 1" installed arch and they retain the long rear segment, and come with less leaf count and thicker leaves. Rates are some what limited, but when the wheel rate is calculated out and a rear sway bar added, they tend to match big t-bar and s-bar rates that are available up front rather nicely.

Yes, your cuda has a 1.67 degree offset in the front. Later B bodies have a similar offset on in the back and FJM bodies cars have an offset similar to Cudas. Afco even supports this type of alignment in their technical manuals, so is some advantage to this offset and it is worth retaining if your fabricating all new mounts.

[KillerWolf]

Thanks High Plains. I'm going to go ahead with the original plan. (Hypercos splayed & Caltracs) I guess if the splayed leafs don't provide enough lateral support, I can always add a panhard down the line.
The other question would be, upon my weight requirement calculations (3600# x 50% = 1800 x 50% = 900 div by 4.5 (arch) = 200#)
I believe I need 200# per in springs. Does that sound right? (the Hotchkis & Mopar oval track are 160#) Or should I go with 150-175# & make up the roll stillness w/ a sway bar? I want to have as close to zero arch a race weight (3600#) as possible to increase roll & lateral stiffness.

Thanks again guys, you're the best.

[High Plains Mopars]

Your rate calculations don't seem right unless you've got all your weight perfectly distributed on all four corners. Even if that is the case, then your calculation would be the finalized wheel rate, which is also impacted by the spring location, sway bar usage, and resulting leverage percentages. In stock form with a small block, your Cuda would be 55-60% front weight bias, so depending on your engine, chassis mods, front wheel rates, etc. you may need considerably less wheel rate than you think.

Using the old mopar oval track guide, you can run up to a 1.14 t-bar with a 1.0 front sway bar, and still be in the usable range of a 120# leaf spring, which is what mopar rates their oval track spring sets at.