8 second OEM 4 link drag race chassis setup

[Alky V6]

Getting that extra weight on the RR was a little more involved than I thought it would be.

Today's progress.
Rubber spring seat added above RR spring.
.600" spacer under RR spring.
LF coilover preloaded an extra 1/8".
RB preloaded 1/2 flat.
Weight on RR: Before 764.0 lbs. After 785.8 lbs.
From this point, very small adjustments to the RB (one flat at a time) will be enough to fine tune the weight on the RR.
Tomorrow, raise the LR LCA axle mounting 1.00".

 

[Alky V6]

There is nothing sexy about chassis tuning. Arrrg.

 

[charlief1]

There is nothing sexy about chassis tuning. Arrrg.

There is if you've got a set of scales and knowledge Donnie.:biggrin:

 

[Alky V6]

There is if you've got a set of scales and knowledge Donnie.:biggrin:

Well, I have to agree that having a full set of scales would make this a lot easier, but I'm sure there was a time when fancy electronic scales were not very common and a person had to get by with doing it exactly the way I'm doing it right now.
I have to agree with you that finding out what the weights are is very enlightening, and it is interesting to see just how much a change affects the corner weights. Especially the roll bar. That was very surprising.
I'm going to finish up on getting the ride heights even at all four corners with driver in the car, while reaching my target preload on the RR corner, and having to use minimal RB preload in the process. I think I'm going to have to shave .100" off the RR spring spacer and add a little to the LF coilover to get it right on.
It will be interesting to see how the car reacts with this amount of preload on the RR, and the asymmetrical link settings. I'm going to be real careful getting on the brakes on the top end.

Knowledge is nothing more than part research, and part experimenting. From that you gain experience. Experience then helps to guide your next experiment, which then allows you to gain more knowledge.

 

[Alky V6]

Today's progress.
The RR spring spacer was cut down to a height of .508".
With the RB set to neutral, the RR corner weight is 778 lbs.
With ONE flat (1/6 of a turn) of preload on the RB, the RR corner weight is at the target of 786 lbs. YES!
The ride heights are exactly even in the front, and is 3/32" higher at the RR than the LR. This is with the one flat of RB preload.

Next issue to address is the amount of LF rebound travel. I want to set the LF extension travel so that the RF is reaching the bumper a certain amount before the LF does in a dynamic situation. I think I'm going to shave off 1/8" off the bumper stop on the LF to begin with. This should yield me over 1/4" more wheel travel. Then videos of the launch will guide me on the rest.

To make up for the additional preload weight on the LF during braking, I may need to shorten the dive travel limit on the LF using the height of the bumper stand. I'll look into that if testing shows it to be necessary.

Before I move the LCA axle mounting point to give me my dynamic roll control, I'm going to modify the rear UCAs to give me a little more clearance between them and the anti-roll bar. They're real close right now.

 

[Alky V6]

I may have to invest in some front end travel sensors. I can see where that information could prove very useful in evening up the rear tire loads during a particular section of the run.

 

[Alky V6]

The front rebound travel limiters are now set in a manner that will have the RF wheel off the ground 3/4" just as the LF is leaving the ground, assuming the front end lifted evenly side to side. I'll leave it like that until I have some video to study.
With the rubber bumpers in the picture, it makes the rate of load transfer a little more interesting.

 

[Alky V6]

The LR LCA axle mounting has been moved up one inch.

Time for a test run!

 

[charlief1]

See if you can get a video of it Donnie. That may help some.

 

[Alky V6]

See if you can get a video of it Donnie. That may help some.

That's the plan.

 

[Alky V6]

I think I figured out a simple mod I can do to the roll bar mounting that will reposition the RB without having to do any cutting and welding. I'll post details of the mod.

 

[Alky V6]

Roll bar before placement modification.

 

[Alky V6]

The links I made up to reposition the roll bar.

 

[Alky V6]

The roll bar repositioned.

 

[Alky V6]

Done. I'll be double checking my corner weights, in case the control arms were resting on the roll bar.

 

[Alky V6]

www.racetec.cc/shope/tim.32.htm
Page 33 of the table of contents is the spreadsheet I used to setup the preloading and asymmetrical link arrangement of the car.

The difference in LR to RR static spring preloading is 66 lbs. favoring the RR. This is along with the use of an asymmetrical link arrangement.

What I thought was interesting was the amount of static spring or spring/RB preload that would be needed using this spreadsheet if the 4 link arrangement had been symmetrical and without the help of using different anti-squat percentages for the left and right sides.
Using a symmetrical link arrangement would have required a preload difference between the LR and RR of about 200 lbs.
It will be interesting to see how this spreadsheet works out.

 

[Alky V6]

I drilled another hole in the left LCA axle bracket. This gives me the following choices of AS% for the left side; 62, 82, 99, 118.
The right side LCA axle bracket still has only 2 holes that give me the following AS% choices for the right side; 96, 121.
Testing this weekend will start with 62% AS left side, and 121% AS right side. I suspect that if I decide to make any AS% changes at the track, it will only be on the left side. And, I won't need to go any higher than 99%.

 

[GARY HARVEY]

but.. is it on a string?

I'm surprised you have not located someone to get you headed in the right direction.
Do you not have a chassis guru in your neck of the woods? We have a couple of them here in my area (they both used to work under the same roof).
Lots of stuff to getting one to go straight, including having the assurance the hard parts are in alignment.
I'll bet you a steak dinner you will be a happier camper letting a journeyman chassis expert do his thing.
Please don't take this the wrong way, Gary

 

[Alky V6]

I'm surprised you have not located someone to get you headed in the right direction.
Do you not have a chassis guru in your neck of the woods? We have a couple of them here in my area (they both used to work under the same roof).
Lots of stuff to getting one to go straight, including having the assurance the hard parts are in alignment.
I'll bet you a steak dinner you will be a happier camper letting a journeyman chassis expert do his thing.
Please don't take this the wrong way, Gary

Once you start researching how to set up a chassis, you find out that it's really not rocket science. In fact, from this point forward, it's going to involve studying the videos to see what the car wants, anyway.

I'm just too much of a hands on kind of guy to not try to do this myself. This is the kind of stuff I really enjoy. Diving into a new area of knowledge and learning more about what it's going to take to get this car to it's best possible shape. If I hit a wall with a problem that I just can't figure out, then that's when I'll look for some help. Not before, though. I'm not known for throwing in the towel very easily.
BTW, there are a couple of chassis gurus that are local. When I think I've done all I can with the chassis setup, I'll have them take a look at it. It sure would be rewarding to find out from them that I've already done all that can be done.

Student for life.

 

[charlief1]

Fly me out for a visit and we can get it set up the way you want Donnie.:biggrin:

Just busting your chops but you really are learning the hard way. Wish you were closer because I'd sneek over for a visit and help you out.