Chassis guys please help with my mopar race car (scale ?)

Tech questions that don't fit above forums

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BillyShope
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Post by BillyShope » Mon Dec 01, 2008 7:32 am

A sneaky trick with torsion bar equipped Mopars is to use a higher rate torsion bar at the right front than at the left front. No tech inspector is going to catch that, and, even if one does, I doubt if the rules cover such a modification. With the adjustability of the torsion bar, you can easily bring the car back to equal rear tire loading on the scales.

But, with the high rate spring at the right front, most of the weight transfer is going to be pulled from that corner during launch. And, since the sum of the right side tire loadings must remain constant (otherwise, the car would be rolling over), that means most of the weight transfer will be dumped on the right rear, tending to cancel the driveshaft torque's tendency to unload that tire.

Consider the reason for that Corvette's low 60 foot: It's got an IRS, so the driveshaft torque has no effect on rear tire loading. The closer you can get to equal rear tire loading during launch, the closer you'll get to that Corvette's 60 foot.
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Post by Tom Cannon » Mon Dec 01, 2008 7:51 pm

Billy I've read over your website and it makes my head hurt.Lots of good info in there.I've calculated I have about 500 lbs of force that my tires can't handle.LOL

As the car sits right now it has .810 torsion bars in it which is what Chrysler refers to as thier "drag bars".So are you suggesting I should install a thicker bar on the drivers side and wind the death out of the passenger bar?

I was also thinking about dumping some unsprung weight.I thought I would buy a set of Calverts split mono leafs and get them with the 20 inch front segment (SS spring).Caltrac bars are not legal. Any ideas about this? Different spring rates are available.The car being a stick has me concerned the spring will go insane on the starting line.Just a thought.It sure would be nice to dump 50 lbs.

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Post by BillyShope » Mon Dec 01, 2008 9:52 pm

Tom Cannon wrote:So are you suggesting I should install a thicker bar on the drivers side and wind the death out of the passenger bar?
The load on the left front bar would remain the same, so I don't know what you mean by "wind the death." So, if all you're going to do is install a higher rate bar at the right front, you won't be touching the left front. You'll merely adjust the right front until the rear scales out equal.

If you've read the pertinent page on my site, you know that I normally recommend 2 new bars with the left front having a lower rate than original and the right front a higher rate than original. The idea is to keep the front roll stiffness as close to stock as possible. (This is for a car that's also going to be driven on the street.) But, since it sounds like you already have a low rate spring on the left front, you'll only need to go into your dealer's "race" catalog and select a high rate spring for the right front. The spreadsheet at my site will help you in your selection.
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Post by Tuner » Tue Dec 02, 2008 5:10 am

I think you should use the clamped Mopar multi-leaf springs and a pinion snubber. You need the strength of the laminated spring pack. I realize the Mopar SS springs came with clips that only aligned the front segment leaves and allowed them to slide, but I think clamping the front leaves tight is what to do.

Mr. Shope, is there a reason that scheme is undesirable or impractical? I’ve done it several times in the last 40 years and the result has always been good. I realize it increases the rear roll stiffness, but isn’t that acceptable or even desirable in a drag car? I think it works better than slapper bars.

I want to say something profound about this http://www.motorsportsvillage.com/carofmonth.html
but all I can think of is “Thanks”. I have no idea how many megaphones I rolled in HS metal shop, but you guys were some of the inspiration. The articles about ram tuning in Hot Rod by a Mopar engineer that had the math in them and a local guys 300G were some more. Pencil and paper and a slide-rule, a handy motorcycle for road testing, life was good. I guess the “Thanks” is for the inspiration.

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Post by BillyShope » Tue Dec 02, 2008 7:34 am

Tuner wrote:
Mr. Shope, is there a reason that scheme is undesirable or impractical?
Just wanted to make it clear to other readers that Tuner is talking about the clamping of the rear spring and not the torsion bar business.

Nothing wrong with this, Tuner, and, yes, it is desirable to increase the rear roll stiffness IF you're not using some other means of canceling driveshaft torque effects (such as the front spring rate trick described earlier). This is what an anti-roll bar (ARB) does, of course. The manufacturer of the ARB warns that it should be disconnected when the car is driven on the street, however. Greatly increasing the rear roll stiffness should always be done with caution if the car sees street service.
Tuner wrote:The articles about ram tuning in Hot Rod by a Mopar engineer....
You realize that was I, don't you? The article was actually written by Steve Magnante, the Hot Rod Technical Editor at the time. I only provided the description of how ram tuning "works" and, of course, the equations.
Oh, yes. I also served as a model for one of the pictures. Didn't have to wear a bikini, though.
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Post by Tom Cannon » Tue Dec 02, 2008 8:08 am

"We eventually agreed that we wanted a Chrysler powered car and that we wanted to compete in a class that was dominated by high specific output Chevy powered cars."

So after 50 years not much has changed.

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Post by Tuner » Tue Dec 02, 2008 6:42 pm

Billy, my memory has always associated you with the Ramchargers in general, mostly from articles about the Max Wedge cars, so for my memory’s sake I hope you were in those. I recall there was a ram-tuning article in `59 or `60 about the long ram and then again later with the Max Wedge deal and then one about the Hemi in the altered wheel base cars with long intake tubes for a TorqueFlite and short ones for a stick. Was that you that came up with the part-throttle bypass for the Hilborn so it would work with a torque converter?

I don’t remember specifically who was mentioned as much as the principles of the math that inspired a friend and me to make a ram manifold for a 312 Ford with a Crower U-Fab kit, longer pipes and a mailbox plenum. We both worked at a speed shop that was a WD for Holley and the 1850’s only cost us $24 so that’s how much some things have changed in the last 45 years. Seeing as how the $24 could buy 100 gallons of gas I guess the only real change was a new carb in those days would actually work.

Are you saying the stiffer rear anti-roll and the offset front spring rate shouldn’t be used jointly? I understand more rear anti-roll needs more in the front to maintain the desired balance for cornering but I never pondered the deal for drag racing where things are compromised for maximum straight-line acceleration. The Super Stock springs and the Hemi cars, etc. had bias in the rear springs, an extra leaf on the right, or an extra half-leaf in the front on the right, and different length leaves on either side. Didn’t you guys ever bias both ends of the car? How would a normal mortal figure out the program you guys were up to with the biased spring packs like the SS springs to make his own?

Let me guess. Sort of like the traction dyno, put the car on scales, chain it to the floor, apply torque to the pinion and then what, measure how much each spring pack flexes from the static and try to balance them for some condition of torque?

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Post by BillyShope » Tue Dec 02, 2008 7:54 pm

Tuner wrote:Was that you that came up with the part-throttle bypass for the Hilborn so it would work with a torque converter?
No. I missed that article and I'm not certain I would agree with it.
Tuner wrote:...the 1850’s only cost us $24...
The first Ramchargers car (the High&Mighty C/A) cost each Ramchargers member about the same amount of money. Amazing what happens to prices when the government printing presses start humming. And, it's really going to get ridiculous in a couple of years.
Tuner wrote:...put the car on scales, chain it to the floor, apply torque to the pinion and then....
And then forget about the changes you've made, look at what the traction dyno is trying to tell you, and figure out what more you can do to equalize rear tire loads. It's unlikely that you're going to apply enough chain tension to completely unload the front, but you can gain enough information from 2 or 3 lesser chain loads to closely estimate the rear tire loads for any value of weight transfer.

Increasing rear roll stiffness, relative to the front roll stiffness, can NEVER, in itself, provide equal rear tire loading during launch. This is because there will always be some front roll stiffness.

If you could find front springs with the proper rates, you could have equal rear tire loading for any value of driveshaft torque. Unfortunately, you'll never find exactly what you need in the parts catalogs.

So, with either an ARB or the front spring rate trick, you'll have to use the traction dyno and some static preloading to make up the difference. But, you'll at least have minimized the necessary static preload.

And, yes, you could use the ARB and the front spring rate trick together, but it's usually easier and cheaper to simply use the front spring rate trick and crank in a little cross corner static preload for the fine tuning.
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Post by Tom Cannon » Tue Dec 02, 2008 10:54 pm

Looks like these days only 2 bars are available. A .920 and a .960 so I have a 50/50 chance of getting the right one. The .810s have been disco'd :cry:

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Post by BillyShope » Wed Dec 03, 2008 8:41 am

Tom Cannon wrote:Looks like these days only 2 bars are available. A .920 and a .960 so I have a 50/50 chance of getting the right one. The .810s have been disco'd :cry:
Why the downcast look? I think you're in great shape. You already have the .810 on the left side, so install the .960 on the right. That should get you very close.

(For those mathematically inclined, the torsion bar's spring rate varies with the diameter to the fourth power. So, the rate ratio...between the .960 bar and the .810 bar...would be (1.97). The spreadsheet on page 16 of my site gives an answer in terms of the spring rate difference divided by the spring rate sum. This is equivalent to (C - 1) / (C + 1), where "C" is the rate ratio.)
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Post by Tom Cannon » Wed Dec 03, 2008 11:15 am

The down cast look is due to the fact that I have 30 cars. :lol:

Billy, would you have a flow of diagnosis for say a new race car? By that I mean if I were to build a new car what would be the order in which things would be weighed,measured and calculated?Before the car moved under it's own power?

Also, do you have any thoughts on the monoleaf with the 20 in front segment?And when I install that 960 bar on the righth side will I be able to get the car to sit level and still achieve the proper rear tire weights?

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Post by Tuner » Wed Dec 03, 2008 1:39 pm


Tuner wrote:
Was that you that came up with the part-throttle bypass for the Hilborn so it would work with a torque converter?

Billy Shope wrote:
No. I missed that article and I'm not certain I would agree with it.
I may have used the wrong term “part-throttle bypass” but the memory is of an addition of something in the form of a bypass to make the Hilborn more functional with a torque converter and my recollection is credit was given (in the article) to a Chrysler engineer for the solution. Maybe it was a high-speed bypass? It was something new at the time (`64-5 ?).
Tom Cannon wrote:
Looks like these days only 2 bars are available. A .920 and a .960 so I have a 50/50 chance of getting the right one. The .810s have been disco'd
These guys http://www.firmfeel.com/ have torsion bars http://www.firmfeel.com/torsionb_a.htm
Lots of Mopar suspension stuff there.

I have no experience with the particular mono-leaf you’re referring to without the rest of the system intended to be used with it, but for drag racing the GM mono leaf on Camaro and Nova is like attaching the axle to the car with bungee cords. Without some other traction aid it’s absolutely worthless. I thought you can’t use traction aids?

An experience everybody needs is a 4 spd. 375HP 396 Camaro with mono-leaf right off the showroom floor. After the Corvair debacle I don’t know how that combination ever saw the light of day. It would be a lawyer’s dream in this age.

Why spend your money (unless you’re printing it like the govt.) when you already have a set of springs? Make some clamps and use a pinion snubber. The car came with clamps (clips) on the springs and a pinion snubber so they can’t call this an add-on.

I see the information in the Mopar Chassis Book as cake and the knowledge and information in Billy Shope’s website as really good frosting. He graciously provides it for free so you can use all you want. Let them eat cake.

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Post by Tom Cannon » Wed Dec 03, 2008 2:20 pm

Well first thing is my springs are beat.They are the mopar Extra HD repop 6 pac/hemi spring.They are 5 yrs old and they are bowed right before the front and rear eye.They have no arch.They have been clamped for as long as I can remember.I'll bet they have 5 clamps on them.I'm not talking about the factory ones either.

I thought the Calverts would be a good way to dump some unsprung weight.They are a split mono leaf so the front and the back can have different rates.I thought I would use the 20 front segment to make it stiffer yet.

I don't know if it would work or not

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Post by Tuner » Wed Dec 03, 2008 3:56 pm

I’ve mentioned the Mopar chassis book a couple of times and you haven’t acknowledged having read the information in it so I guess not? If the book is still available it’s Mopar # P4452791.

It’s the lamination of the spring pack that gives it rigidity, like the difference between plywood and a similar thickness of a single board. I think for the front half of the mono leaf to have as much strength it would have to be at least as heavy. After all, steel is only steel. Is anyone using the split leaf deal without the rest of the device?

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Post by BillyShope » Wed Dec 03, 2008 4:33 pm

Tom Cannon wrote:...will I be able to get the car to sit level and still achieve the proper rear tire weights?
Of course. The adjustment was designed for the full range of bars available, so it's only necessary, as you install the new bar, that you crank in the necessary preload to achieve equal rear tire loading.
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