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Tuning the IRS for drag racing

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Old 05-21-2012, 09:53 PM   #1
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Default Tuning the IRS for drag racing

Im trying to set up my car for drag racing at the track. I want to know what can i do to get the IRS to hook better. Here's what i have so far.

Built 9" IRS
solid cradle bushings
subframe connectors
stock springs (cut to lower the car)
stock shocks (with lowering spacers)
stock sway bar/ end links
BMR trailing arm
BMR Toe rods
26x10.5-16 MT ET streets

The best i was able to do was a 1.9 60' with a 4500 clutch dump so i'm looking to reduce that. One of the things i know i need to do for sure is raise the rear of the car either using stock springs or some other form. What else can i do, it just feels like the car doesn't plant the tires down they sort of just float. It doesn't wheel hop at all so thats not a problem.
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Old 05-21-2012, 10:21 PM   #2
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Its old school but Air Lift Drag Bags do help and they are cheap.
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Old 05-21-2012, 10:25 PM   #3
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yeah i've looked into them, however i don't know if i'm suppose to increase or decrease the spring rate.
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Old 05-21-2012, 10:40 PM   #4
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How much air are you running in the slicks?
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Old 05-21-2012, 10:51 PM   #5
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I started at 17 psi and worked my way down about 13.5 was the sweet spot.
What do you think about raising the rear of the car using stock cts springs. I imagine they are a little taller than v springs but are also softer.
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Old 05-21-2012, 11:54 PM   #6
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Can you fit 16" rear tires? Will it clear the brakes?
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Old 05-22-2012, 12:16 AM   #7
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16's fit with smaller brakes.
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Old 05-22-2012, 12:28 AM   #8
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Quote:
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I started at 17 psi and worked my way down about 13.5 was the sweet spot.
What do you think about raising the rear of the car using stock cts springs. I imagine they are a little taller than v springs but are also softer.
Id try and put a taller tire on the car to start. The extra sidewall should help with the launch. Might be worth seeing if someone has a set you can try out and if they help grab some ET Drags next go round.
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Old 05-22-2012, 08:06 AM   #9
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Do you have the FE4 or FG2 shocks? Wouldn't shocks with a stiffer rebound help keep the tires planted? I don't really know anything about setting up a suspension for drag racing but it just seems like that would help.
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Old 05-22-2012, 09:28 AM   #10
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Quote:
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16's fit with smaller brakes.
So, you put the standard CTS brakes on?
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Old 05-22-2012, 10:46 AM   #11
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Yeah im going with a taller tire, I have a set of 28x11.5-16 et drags that i want to try. However i have to raise the car back up to fit them and i have to modify the trailing arm since they are wider and they rub.

About the shocks, i actually don't know what kind i have. Also not sure if a stiffer shock works better.

Yes i am running cts calipers and rotors in the rear.

i have a launch control and WOT box im about to install to see how that helps.

Thanks for the input so far guys lets keep the discussion going i'm headed to the track friday again and i want to mess with it during the week.
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Old 05-22-2012, 11:23 AM   #12
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what are you et's with a 1.9 60' and 402 procharged
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Old 05-22-2012, 12:10 PM   #13
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http://www.highperformancepontiac.co.../photo_07.html
I would give that a try should help, stiffer shocks ( faster rebounding) should also help. Cts springs are a lot thinner, I have a set laying around if you are interested but IMHO it's a waste of money
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Old 05-22-2012, 12:26 PM   #14
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Quote:
Originally Posted by NEED MO POWA! View Post
Yeah im going with a taller tire, I have a set of 28x11.5-16 et drags that i want to try. However i have to raise the car back up to fit them and i have to modify the trailing arm since they are wider and they rub.

About the shocks, i actually don't know what kind i have. Also not sure if a stiffer shock works better.

Yes i am running cts calipers and rotors in the rear.

i have a launch control and WOT box im about to install to see how that helps.

Thanks for the input so far guys lets keep the discussion going i'm headed to the track friday again and i want to mess with it during the week.
Disclaimer, I don't do drag BUT I do dabble with shocks.

From what I've gleaned you want softer rebound and stiffer compression for launches. I know a lot of drag guys use qa1 shocks as they offer adjustment for comp/rebound. Plus they're relatively cheap. Going ultra stiff on shocks may not help you much and may make things worse.

Check also that you've not blown your shocks.
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Old 05-22-2012, 12:32 PM   #15
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Being lowered is really hurting you. I don't know if anyone makes adjustable shocks for the front of our cars, but the front has to lift and the rear has to squat to transfer the weight properly. OE STS springs may be the way to go since they are softer on a heavier car...don't know about the shocks though.

I would also try to add some positive camber at the rear wheels so that when you launch the tires stay flat on the ground rather then going negative camber when it squats.
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Old 05-23-2012, 09:42 AM   #16
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I would try to launch the car at 3000 to 3500rmp and rides out the clutch,too much power at line cause wheel spins,thats all was help me on a manual car,a launch controler will help u out at lots
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Old 05-23-2012, 01:49 PM   #17
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You have a KARs subframe connector or something else? Pics?
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Old 05-23-2012, 02:23 PM   #18
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Quote:
Originally Posted by DMM View Post
Being lowered is really hurting you. I don't know if anyone makes adjustable shocks for the front of our cars, but the front has to lift and the rear has to squat to transfer the weight properly. OE STS springs may be the way to go since they are softer on a heavier car...don't know about the shocks though.

I would also try to add some positive camber at the rear wheels so that when you launch the tires stay flat on the ground rather then going negative camber when it squats.


Both things I was thinking while reading.

Weight transfer and tire contact are keys to a good launch.
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Old 05-23-2012, 03:18 PM   #19
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Yeah i realize being lowered is hurting me , that's why i'm looking to raise the car back to stock height. With it being lowered the car has more negative camber, raising it should help a ton to get proper contact patch. would it be beneficial to raise the front also?

Anybody have some stock cts v springs laying around?

The subframe connectors were part of the madman rear end package, they are welded to the rear cradle and bolted to the front subframe.

here are some pics:






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Old 05-23-2012, 04:32 PM   #20
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I like the subframe connectors I plan on doing something like that on mine
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