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Discussion Starter #1
Car is a 2000 Trans Am, 400 hp on motor, 200 shot. Long torque arm, TRZ relocation brackets. Rear suspension is all rod ends.

If I understand correctly, the only way to change the instant center is to change the length of the torque arm. Some people say there are minor changes from adjusting the front of the torque arm up and down. So would moving the front of the torque arm up or down transfer more weight to the rear wheels?

From research, I set the car to -2 pinion angle, torque arm 2 degrees down hill to the front, and lower control arms 2 degrees down toward the rear end. This has netted me a best of 1.43.

I'm getting ready to check everything again and was wondering if these angles should be in relation to the chassis or the ground. It makes more sense to me for them to be in relation to the chassis. May car sits with some rake to the front and with the lower control arms set at 2 degrees toward the rear end it's about a 4 degree difference to the chassis. The torque arm at 2 degrees down hill to the front is parallel with the chassis.

Thanks for any help.
 

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First off get the pinion angle set to zero it's just creating a driveline bind, no need for it that's for leaf spring cars.

The lower control arms, should be pointing up from the rear going forward somewhere around 2 to 3 degrees depending on the car.

Where is the ride height of the car, measure the center of the wheel openings to the ground, so we know what kind of rake you have in it.

What tire are you running, slick, radial, and how is your track prep? Nitrous all come on at the hit or is it progressed?

You have 9 second power and depending on gearing/converter and weight of car you should be able to see mid 1.3 with a good level of consistency at that power level, I assume this is a small built LS powerplant with a behind the TB type plate kit, or something similar?
 

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Discussion Starter #3
I will get wheel well measurements next time the drag wheels are on.

Tires are MT 275 60 15 et drag radial, track prep is touchy. Some tracks great, some not. I have the car where I can leave on 100 shot. Working on the progression of the second 100. Both kits on NOS mini.

3.73 rear, PTC 4000 nitrous converter, 3500 currently with driver(getting ready to install wolfe 6 point, crotch strap bracket, and 5 point, so planning on 3600 race weight), car has two wet nozzles currently on 53 jets in both. Best is a 10.28 on a 47 jet 1st stage and 53 jet 2nd stage, with a 1.46.

Current tune in mini to try next time is: leave on 100, second stage delayed .6, start 40%, build time .4, end 100%.
 

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Discussion Starter #5
Rear is competition engineering set to 50/50 with cut stock springs. Front is a lowering spring on stock shocks. shocks are my next area to address. It spins if I try to bring the second stage in too fast, I was only delaying the second stage .2. Front would come up, then down and spin.
 

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Discussion Starter #6
I also have the BMR xtreme anti roll bar on the outermost holes. I'm going to move that the stiffer holes as well because the car is still rolling over some.
 

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Try the inner holes on the sway bar that may help, shocks with a 275 lb (alum motor) or 300 lb (iron motor) would help a lot on the front, a good double adjstable on the rear would be a massive help as well. Call Madman and get the afco's with his valving, convert the rear to coil over while you're at it so the rear springs can be done with a 150 lb or whatever madman recommends... That's going to be what makes all the difference. Once you have the geometry right you will have to have shocks that can control everything right.


Fwiw at your power level you should be able to leave on 1st jet and bring 2nd in .2 after starting at 70 pct and be all in by .4 with absolutely no issues... Once you have the car working it will take all that easily.
 

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Defintely need some double Adjustable shocks on that thing. With the long torque arm its most likely not separating enough to keep the tire down. Also, have you plotted that thing yet at ride height??? Torque arm down LCA pointing up sounds like a bind to me........those need to intersect at the closest position possible IMO. Makes for a much happier application of power.
 

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As long as the TA has a sliding front link then it won't bind.

Besides the shocks that has already been mentioned, most likely what is happening is that you're hitting the tires too hard off the line (too much antisquat), it's planting hard and then after a little bit you loose traction. If you have LCA relo brackets on it, try moving them up one bolt hole and see if it's better.

Otherwise as has been stated, pinion angle doesn't have anything to do with traction, and you want it as neutral as possible. Driveline angles should be measured relative to the driveline (typically off of the engine/trans/output shaft angle, and you should get the the rear U to mirror the angle of the front one as close as possible). Suspension should be measured relative to the suspension, and height of the front of the TA should have nothing to do with IC or traction (If it's a sliding link it's plane for calculating IC is a vertical line through the sliding link, if you can picture that you can see that it's height has no effect on suspension action), and you can only adjust anti-squat/instant center by changing the angle of the LCAs or by changing the length of the TA.
 

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Discussion Starter #10
Thanks for the help guys. I have not plotted the car. I'll work on some shocks. Just dropped money on the roll bar to keep it safe. Sounds like I'll set the torque arm parallel to the chassis. Set the lower lower control arms back up some, maybe 2 degreen down in back compared to the chassis. Stiffer setting on the swaybar. I'll just have to tune the nitrous to what the chassis will take for now. I do understand how to set driveline angle. So some have said no negative pinion just set the pinion parallel to the crank, what's the consensus here. Hitting the tires to hard makes since because I wasn't having spinning issues last year with a stock swaybar. Put the stiffer bar on and longer relocation brackets with the lca in the bottom holes and now its spinning.
 

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Car is hitting the tires and unloading out, that's shocks, may be the only thing that you can do to hold the hit on the tires.

Tq arm angle will change the intersect point and short vs long will change how far back the intersect point is. Madman tq arm with it's ability to raise and lower both the front and back of the arm gives a lot of options.

Do what you can with the power management until you can put some shocks on the car. Just go double adjustable whatever you do, start with the rear and then the front. That will make the biggest difference.

2 to 3 degrees down on the control arms will likely be about where you end up, maybe 4 due to chassis weight but a light car will stand up with that much anti squat very very easily.
 

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Discussion Starter #12
So what would you recomend for torque arm angle? Front up or down? The car has never even pulled a wheel up even on the 1.43. It even spun on motor at mir a month ago and car has never done that. After talking through it ,it must be to aggressive lca angle. That would also explain why I had to keep going down on psi to get a marginal pass. It's got to be bouncing the tires. Does 18 psi in the 275 60 15 sound good?
 

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18-19 is what everyone I know runs in the 275 tires, I would think that's probably fine.

To me it sounds like the car is hitting the tire and then as the front starts to settle it's unloading the rear and causing the spin, stopping this is a function of shocks, rear's need to extend quickly to plant tire on the track and then the compression needs to be extremely slow so that it can't unload the tire. Front needs to not raise too much as this gives too much motion to cause weight shift, which will unload the tire.

I would try 2 to 3 degrees of lca angle, no pinion angle, put your stiffest setting on the swaybar, you don't need to compound the issues with the chassis rolling too much.

Now tq arm, you are going to have people on here that will tell you that moving the tq arm up and down on the front mount won't do anything, so you can believe what you want. But from my experience on slicks, this is my findings on this:

Tq arm starting in the middle of adjustment, if the car seems to spin at the hit, I found raising the front mount upwards, would make the initial hit on the tire harder. However it would be more prone to unloading the tire down track, and this made for stiffer shock settings needed. If you find with the tq arm in the middle adjustment it seems to spin a little bit out, lowering it seems to make the tires plant a little less at the hit, but they seem to stay planted better down track.

Now lca angle is going to do similar things but the tq arm seems to effect traction down track more than just at the initial hit where control arm angle seems to have the largest impact.

I can tell you that if the lca angle is at about 4 degrees downward and the tq arm is in the upper hole, on a slick you will take the car and put it strait on the bumper. Been there done that. I was able to stop this by lowering the tq arm to 1 hole from bottom and decreasing lca to 2 degrees.
 

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Discussion Starter #14
Thank you all very much for the info. I'll definitely try some chassis changes and try to get some good shocks on the car.
 

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Discussion Starter #15
Went to the track last night. New best 60' 1.41 and new best 330. Got out of it after that as the old 4l60e was having trouble with the 2-3 shift. The car hooked great and the track was not that great. The front would rise and stay there. This was also carrying the extra weight of the roll bar. I decided to leave the torque arm and pinion alone for now. I put the sway bar on stiffest setting with 1/2 round of preload in the passenger side. I moved the lca up one hole. They had about 4-5 degrees of down angle compared to the chassis. They are now at 2-2.5. I left on the first stage and had the second setup as .6 delay 30 start .4 build to 100. I could tell I could have easily brought it in sooner.

Next question concerning the pinion angle. Setting it at zero. Can we assume there is no flex at all in a long torque arm?

Thank you all so much. Left the track very happy.
 

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There's no real flex in the arm, so you can match the angle of the Trans with the rear, essentially making it zero for minimal driveline losses. If you can leave on one and start bringing the 2nd in .2 out and have it all in by .2, you should get the 60's down a bit more doing that, at which point it might take more on the first stage as well.

Glad it worked out, if you want to race the car a lot best advise I can give is dump that 4ljunkie transmission. I've never seen one last any reasonable amount of time in a race car and everyone that's racing with one has a spare they're swapping back and forth between while one is being fixed, don't believe all the stories. th400 and forget it unless you're daily driving it.
 

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Discussion Starter #17 (Edited)
I do daily the car. Once it takes a dump I probably will go with a 400 anyway. I already have the second stage turned to only a .3 delay for the next time out. I will give the pinion at zero a shot.
 

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Sounds good. If the car takes turning the 2ns stage on quicker I would change the build to .2, so it's on fast. Sooner you can get it all on the better it's gonna go.

I used to turn a single 65 on at the Trans brake hit when I had a 402 ls motor in my car, if I had a progreessor or anything like that back then I would have put a 78 pill to it and ramped it in, any more than the 65 and the car spun with the front end off the ground. Kind of hairy.
 

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If you're concerned about it flexing go 1/2* or so down, but it's not going to flex much unless something is wrong, but again, it won't make any difference in your launch, just the durability of driveline parts.
 
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