Drag Race Rear Suspension...

[Playdough]

I have a 04 Pontiac GTO that I like to drag race. Its making around 345 rwhp though an A4. I'm wondering what the trick is to getting the Monaro/GTO to hook hard. There doesn't really seem to be a real good idea in the states on it yet, still alot of trial and error going on. I was hoping that a few of you drag race guys could help me out with sharing your setups, or what you found that works and doesn't work.

Some of my thoughts have centered arounda very stiff rear suspension and a very soft front suspension to use the springs as almost a pivot point and get the body to the push down on the tires getting them to stay more upright. Another thought I have had is a stiff rear and a stiff front with travel limiters restricing front end raise and rear squat, once again keeping the tires more upright.

This is my first experience trying to launch an IRS car. So any help or tricks or tips that I can get from the guys that have the most experience with these cars would be great.

Thanks

[ratter]

I havn't raced an IRS rear ended car, so my info may not be correct, but I would soften the front with soft springs and use 90/10's and remove the sway bar.
The rears I would play with the alignment to get the tyres as straight up and down as possible (more rubber on the track) and use air bags in the rear to stop it squating.
Rely on the weight transfer from the soft front to place more weight onto the rear tyres.
If the back squats, it appears to be pulling the body down, but what it is doing actually trying to pull the wheels closer to the car ( gravity keeps it on the ground) which can be taking effective weight from the rears.

[Oztrack Tuning]

Mine has lowered and slightly harder than FE2 springs - but has adjustable Konis on rear (that are valved for a lighter car - so they rebound slower as well - but the adjustament is only on bump). I have tried to make the shocks allow the car to come down and stay down in the rear - but not so much that their is extra negative camber that causes trouble. ....to hard and it spins - too soft and it squats too much and can spin inside edges....JUST hard enough in the rear is the key i think....may be going with 90/10s up front soon or some adjustable shocks.

The front is stock but shocks are old and soft.

My car has done 1.622 and consistent 1.64 with MT ET Street Radials 235/60 x 15 and a Yank SS3600 stall

http://www.oztrack.com/clubsport/wheelstandwewonder.jpg

[Playdough]

Keeping the rear of the car stiff I'v thought has always been what I thought would work best. What I wonder though is if the rear is stiff and front is soft, if the middle of the car would act as a pivot point and push the weight down on the rear tires and plant them?

oztrack,

Do you know what the spring rates on the FE2's are? Also, on the Koni's what kinda settings do they have and how many do they have? I noticed also that you are running a 15 inch wheel, did you have to do any clearencing on the rear brakes to get those to fit?

Ratter,


Funny you mention airbags, me and a buddy of mine with a GTO was just thinking and talking about the same thing.

[Oztrack Tuning]

Just some ideas
- air bags will be quick on rebound and will unload the rear tyres straight after impact. When the car is 'stalled up' its taildrops putting more weight on the rear at launch - at launch is squashes lower and aids in weight transfer - any rapid upward movement could make the front come down quick.
- M6 or A4 with HS - may be big difference in setup - as its the HS-A4 that pulls their tails down pre-launch.
- I think fronts being 90/10 make more difference than anything.
- I dont know the spring rate but mine are a bit harder than sporty stock (FE2) on the rear only and are a bit lower than sporty stock - front are luxury stock non Fe2 - full length. My rear konis are valved for the calibra which is a few hundred kg lighter car.

[Playdough]

Do you believe that keeping the rear of the car down in a "squated stance" and the front end up is key to a quick short time? So a spring and shock combo that keeps the rear pulled down is good or just a combo that is slow on rebound?

With the 90/10's that is helping slow the front of the car coming down correct? Helping keep the rear of the car planted and to keep from un-loading the rear tires, correct?

Sorry for the all questions but you guys are the experts when it comes to these cars, and I'm looking for all the help with them I can get.

On the 15's what kinda of brake clearance do you have, and what did those come off of? Also what is the total tire height?

[PanVS]

Is squat good, or undesirable, for acceleration? Im trying to decide whether i should change to heavier rate rear springs(to reduce squat).

[OZI355]

i thought squatting is losing time as it goes down and not forward

[Nutter]

i thought squatting is losing time as it goes down and not forward

your right but it soaks up shock keeps tyres gripping, time loss can overcome by shallow staging and also by taking off a wee bit earlier when the tree comes down.

Test and tune days will help ya get the thing right

[Oztrack Tuning]

There is no time loss.
Mine has now done 1.551 with 3.73 gears and just a 3600 stall.

The timer doesnt start until the car moves out of the beams. The peak G force doesnt happen until 1m after the car has moved forward.

The squatting probably does protect the drive train so does the pop-up front. Last time they were inspected my rear axles looked like new and that was after about 180 passes.

Too much squat is bad only if it effects the contact patch of the tyres.

[dadem0n]

There is no time loss.
Mine has now done 1.551 with 3.73 gears and just a 3600 stall.

The timer doesnt start until the car moves out of the beams. The peak G force doesnt happen until 1m after the car has moved forward.

The squatting probably does protect the drive train so does the pop-up front. Last time they were inspected my rear axles looked like new and that was after about 180 passes.

Too much squat is bad only if it effects the contact patch of the tyres.

I know how good the standard FE2 is with just a set of 90/10s :yup:

Do you think you could see an improvement with slightly lower (1") softer springs front and rear (eg 1" lowered V6 springs)??

[Nutter]

There is no time loss.
Mine has now done 1.551 with 3.73 gears and just a 3600 stall.

The timer doesnt start until the car moves out of the beams. The peak G force doesnt happen until 1m after the car has moved forward.

The squatting probably does protect the drive train so does the pop-up front. Last time they were inspected my rear axles looked like new and that was after about 180 passes.

Too much squat is bad only if it effects the contact patch of the tyres.


Your right no time lost becuase its not triggered till you pass the beam but reaction times suffer, thats why I said to stage shallow and hit it earlier, at least thats how I doit, works well for me.

[Oztrack Tuning]

Reaction time is geared to the lights coming down. So that doesnt matter. But its important to be 'just in' on the second white light.

There is no disadvantage with squatting - as long as the contact patch is still wide - due to good camber.

Below are some 1.57-1.58 60 footers and 11.55 runs.

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[markone2]

I know how good the standard FE2 is with just a set of 90/10s :yup:

)??


1.47 good on drag radials :) .......don't play with the ride height

[dadem0n]

How did I know you were going to say that :lol:

Point taken though :yup:

[BOBGEN111]

I have done 1.6ish 60foot with stock exec rear suspension with heavy clutch dumps.

[PanVS]

So leave the FE2 springs in? Are they best for being 'Quick'?

[Dee Jay]

Interesting to see a number of different rear end set ups getting similar 60'?

But on further inspection you will find that the M6 cars benifit from stiffer rear ends and the A4s from softish rear ends.

As for air bags just to correct previous comments the rebnound of them can be controlled by having a slower rebound on the shocks just as you can control the harder springs.

The shocks are there to control the spring rate rebound , just ask Kiwi .
After advising him that his car looked like a Dolphin going down the strip and he should adjust his rebound hey presto .2-3 gain with only that adjustment.

Cheers

[vxls1]

From my experience with a bolt on A4 holden have supplied just the right rear drag suspension setup. Have tried a few different setups only to go backwards and now back with the good old FE2 for 1.56 60fts on the MT drag radials.

Cheers

[dadem0n]

From my experience with a bolt on A4 holden have supplied just the right rear drag suspension setup. Have tried a few different setups only to go backwards and now back with the good old FE2 for 1.56 60fts on the MT drag radials.

Cheers

Interestingly Ive heard this from someone up here in QLD before...... :diddy:

[vxls1]

Interestingly Ive heard this from someone up here in QLD before...... :diddy:

If I had of listened to him in the first place woud have saved alot of time, effort and $!!

[PanVS]

From my experience with a bolt on A4 holden have supplied just the right rear drag suspension setup. Have tried a few different setups only to go backwards and now back with the good old FE2....

Fronts? What works best?

[Oztrack Tuning]

To much squat and you will loose contact patch. A M6 will hi harder and go down quicker - this might make it prone to loosing contact width so it will need firmer springs. However firmness less squat i predict will correlate well with people having lots of breakages. 90-10s up front may help in this area though.

Mine has a little firmer than FE2 springs on the rear BUT the shocks are soft and go down and stay down. Thats the secret!

90-10s up front and softer springs in the front - it would be even better. 5500rpm stall , 4.55 rear end and I reckon these cars could go below 1.400 on the right rubber.

Once anyone has experienced a sub1.60 60 footer you will be hooked. Its like being shot out of a cannon. My car hits the limitter in less than 0.6s on street rubber in 1st gear if i try to launch it the way i do at the track. But at the track it hooks.

[Dee Jay]

Mine has a little firmer than FE2 springs on the rear BUT the shocks are soft and go down and stay down. Thats the secret!

While soft shocks are fine its thier ability to hold the spring in a compressed state that is paramount


My car hits the limitter in less than 0.6s on street rubber in 1st gear if i try to launch it the way i do at the track. But at the track it hooks.Now thats why us M6 drivers get such a BUZZ , dancing around the cabin in the first 3 seconds of the run is frantic :bravo: