8 second OEM 4 link drag race chassis setup

[Alky V6]

Now, here is something that is very interesting. This is back to my present setup. The body is dropped .60" in both the front and rear.
Could the downforce of a wing accomplish a .60" body drop in the rear? I would surely think so.
The problem I see here would be the lack of traction after the launch and before the wing could start working.
Although, the wing could generate enough downforce by the 330' mark with my present setup.
I may look into dropping the rear just 1/4" again and trying that out. I know I tried it before and got some tire rubbing, but that was because the car was doing some skating from side to side too (car got out of shape). I'll have to see again if it rubs with some nice and straight passes.
If I can start out with the car 1/4" lower from the start, the wing will have to do less work to drop the rear down .35".

 

[Alky V6]

My new favorite with the static 1/4" ride height drop in the rear. The light grey lines and numbers showing the car sitting static, and the blue showing the car with a dynamic .80" rise in the front and rear.

 

[Alky V6]

Back to the present setup with the revised .25" lower rear static ride height and a dynamic drop in the rear of .40" and a dynamic lift in the front of 1.4".
Again, the grey number and lines are static and the blue are dynamic.
This is a good example, giving a clue as to why this car has 60 footed so well up to this point.
This also shows a little roll control going on between the left and right side under dynamic loading.

 

[Alky V6]

The next step will be to modify the UCA frame mounting to make it adjustable.

 

[XXQUICK6XX]

I know once I get mine running this will be the next step needing attention.

 

[Alky V6]

Something to ponder.
The CG, neutral line, AS and IC are all very dynamic through the course of a quarter mile pass.
For instance, lets say you've blocked off the front grill, lowered the front end and installed a tall front air dam. This is going to affect front end downforce/lift. Any affect on the front or rearend downforce is going to move the CG. Maybe not a lot, but it will move. Any time the CG moves so does the neutral line and the resulting anti-squat percentage.
How would adding 200-300 lbs of rearend downforce change all these factors?
Front and rear ride heights
CG
IC
AS
How would one adjust the static IC to compensate, or take advantage of all these changes in all these variables throughout a pass? Front and rearend travel sensors suddenly seem to be very important tools.

 

[charlief1]

I'll send you an email later Donnie. You're one of the few that will have an idea of what I'm gonna do to the rear as a whole.:biggrin: Since I can't class race and I'm stuck on bracket I figured that I can do pretty much what I want. My nephew just did it and it picked up .6 in the quarter and I think he had to clean his shorts afterwards. This may be exactly what you've been looking for to ge a little better traction.:smile:

 

[Alky V6]

I look forward to it, Charlie.

 

[Alky V6]

Notes on interesting information I'm running across as I study drag chassis setup.

It has been suggested through testing that peak tire traction (friction coefficient) is realized between the tire patch and the ground when tire speed is about 10% greater than the circumstance of having no slippage between the tire and the ground.
I find this idea fascinating.

The challenge of accelerating a car as quickly as possible involves having all the driving tires carrying equal weight loads. The torque of the driveshaft working against the rearend causes unequal weight loading of the left and right tires. The trick is to adjust the chassis in a manner that gives equal weight loading to both the left and right driving tires at a given driveshaft torque input.

 

[Alky V6]

The more I study drag chassis setup, the more I am completely blown away that my car has succeeded in doing what it has considering that it hasn't been until very recently that I've started getting serious about setting up the chassis. After the upgrades I've done to the car in the past, and the upgrades I'm about to do, I think I'll have all the tools I'll need to push the performance of the car even further. This is very exciting stuff. It's like finding a well of lost horsepower.

 

[Alky V6]

Notes:
The sum of the loads at all 4 wheels much equal the weight of the car.

The sum of moments about any arbitrary axis of rotation must be zero.

 

[sackracing]

Do you have any pics of the front suspension limiter setup? I'm getting ready to go that route.

 

[Alky V6]

Do you have any pics of the front suspension limiter setup? I'm getting ready to go that route.

I'll get some for you.

I've learned that if you are going to have one side front end rebound limiter come in earlier than the other side when the car is rising on take off, it's preferred to have the left side reach the limiter sooner than the right side. This helps put more weight on the right rear tire where it's needed during front end rise. This is a harsher method of dynamically equalizing weight loading of the rear tires, since when the limiter is abruptly reached, it also abruptly changes rear tire loading distribution.

Different spring rates used in the front end can dynamically help equalize weight loading between the two rear tires as the front end is rising. This method gives a much smoother transition of rear tire loading distribution during front end rise. The lighter spring rate being used in the right front.

Note: When both front end tires have left the ground, weight loading is equal on both rear tires. As soon as one front tire touches back down, or one front tire is in contact with the ground, weight distribution among the rear tires is affected.
If one tire is going to be in contact with the ground, it is better to have it be the right side tire. Having only the left side tire off the ground, weight transfer to the right rear tire is better.

 

[sackracing]

I spoke with the chassis guy on Friday, told him I wanted an X275 style setup and he said he would have to add the limiters, but his style includes welding on my new tubular a-arms. I'd rather avoid that if possible.
I have an HR bar on the rear and it keeps the car level.

 

[charlief1]

You're completely right Donnie, but you need to scale the car before you go there. The way the car transfers power to the rear is effected by the way the car sits statically. Once you find where the static weight is then you can use a jack under the front to find out where the weight sits as the front comes up. This will really open your eyes and help you with more traction.

 

[Alky V6]

Other methods of controlling rear tire weight load distribution before and during launch are;

The placement of components in the car, such as having the weight of a battery placed over the right rear tire to apply a preloading of weight on the right rear tire. Although the weight of a battery is not nearly enough to compensate for what is generally needed at the right rear corner.

Weight jacking of the corner springs, again to preload the weight on the right rear tire.

ARB (anti-roll bar). The anti roll bar can be used to apply a preloading of the weight on the right rear tire, but also affords more roll stiffness to the rearend.
One way of controlling weight distribution during dynamic loading of the chassis during launch is to increase the ratio of roll stiffness between the front end and the rearend. This is why commonly a stiffer sway bar, or ARB is used in the rear, while the front sway bar is altogether removed.
An interesting thing about using an ARB. If you use one, it's best to not use it along with other methods of dynamically controlling rear tire weight distribution. In other words, you would not use it with different rate front springs, or front end limiters timed to come in at different times, left then right.
ARBs can be used with weight jacking and component placement methods of preloading the right rear corner.

Another method of dynamically controlling rear tire weight load distribution is using asymmetrical link arrangements in the rear suspension to cause dynamic weight distribution to the rear tires. Generally, this is another method that you would use instead of an ARB.
Any sort of dynamic method of controlling rear weight load distribution between the two rear tires makes it unnecessary, or less necessary to have an ARB.

 

[Alky V6]

You're completely right Donnie, but you need to scale the car before you go there. The way the car transfers power to the rear is effected by the way the car sits statically. Once you find where the static weight is then you can use a jack under the front to find out where the weight sits as the front comes up. This will really open your eyes and help you with more traction.

I understand. I just want to learn how all this works before I put it on the scales. I will be covering the scaling of the car and all the adjusting when the time comes. There are some interesting procedures that can be done with the scales. One being using a wheel chock to create a traction dyno, so that driveshaft torque can be considered in the corner weight loading chassis adjustments.

 

[Alky V6]

Something to think about.

When calculating the location of center of gravity of a car, you are including the weight of the rear axle which is unsprung weight. In the sense of calculating the anti-squat 100% line, subtracting the weight of the rear axle housing would have some affect on the placement of the 100% anti-squat line. If you were to try to figure where the center of gravity of the car is without the rear axle weight included, the CG would actually be further forward and higher from the ground. With that being the case, the 100% anti-squat slope would be steeper, by just a little. Something to consider when looking at 4link software results.

 

[Alky V6]

Playing with the 4 link sim again. I think I found a much simpler solution to my 4 link problem. This new setup retains my present UCA link locations. The difference is in the lower rear control arm mounting locations. Lower by .40 inch. This moves the LCA further from horizontal with the ground, but I've learned that the only reason to attempt a level LCA position is to make IC changes easier with only changes to the UCA front mounting location needed with a level LCA.
Since adjustment convenience for most 4 link cases seems to be the only advantage to making the LCA parallel with the ground, and modifying the UCA front mounting location would be such a pain in the you know what in my case, I'm going to start with modifying and playing with the LCA rear mounting location first.

The first pic is with the rearend raised .6 inch and the front raised 1.6 inch.
The second pic is with the rearend lowered .6 inch and the front raised 1.6 inch.

 

[Alky V6]

The same setup with the rearend only lowered .4 inch. Possibly accomplished using downforce from a wing.