LS/T56 rear suspension upgrades for drag strip launch

[zildjian4life218]

Hey everyone!

This winter I did a LY6 6.0L LS and T56 swap into my 86 olds cutlass. Once tuned it should make around 450 to the wheels if not closer to 475. It has a spec twin disc clutch in it. I am having a hell of a time trying to get the car to launch at the track. Generally just spins. at anything above 3500 and bogs under 3500 and unloads rather violently then spins. Car has a 2 step wired into the clutch pedal to control launch rpm. Tried tire pressure from 12 - 18psi which did not make a big differenc. Either spun or bogged then unloaded. Best 60' was about 2.20 seconds but average was around 2.50 seconds when last year I was running 1.70 seconds 60' with the SBC 350 and TH350 trans. Currently it has 235/60R15 MT E/T street drag radials on it. From what I have read so far they will not work well with the manual transmission and I need to go to a bias ply slick. No problem there will order them in the next couple weeks but I am also curious about springs and shocks.

I do not know if possibly the violent launch is due to the short OEM pinion snubber that is in there or not?

Currently it has some cheap KYB gas-a-just shocks in the front and rear that are maybe 4-5 years old. Springs are 2" drop springs in the rear and 2" up front from somewhere online but basically nothing race or performance oriented and were rather cheap if I remember and also 4-5 years old.

Rearend is a Ford 8.8 from an Explorer that was narrowed and centered and had all the g body brackets welded on in a jig. Also has UMI tubular adjustable control arms upper and lower, and has a 2002 Mustang GT sway bar. I think like 24mm.

Drilve line angle was right around 3* down and I think pinion was up 1*. Not sure if because of the tubular control arms I should now make them match?

Where should I start with this? a lot of people I have talked to and research I have done on this forum and other say definitely a bias ply slick and adjustable shocks. Figured probably different springs as well. HAve an issue right now where it seems like it is leaning to the drive side ever since I did some hard pulls the other day.

The only thing to consider is that this is a street car. I do plan on driving it on the street, and driving it to the drag strip as well as possibly going to some road course events as well. Sort of a triple threat car.

Where do you guys think I should start? I see a lot of people like the bilsteins but I was not sure since they are not adjustable if I should get them or not.

thanks!
Shane

 

[marcar1993]

You say explorer rear, what are the upper control arm mounts that are normally cast into the housing? What style upper arms are you running? Stock g body geometry? A swap kit with instant center relocation? Just adjustable mustang arms?

 

[Texas82GP]

Have you done anything to strengthen/stiffen the chassis? You need to give it some help at that power level.

 

[zildjian4life218]

Have you done anything to strengthen/stiffen the chassis? You need to give it some help at that power level.

I boxed in the frame about 4 year ago and put in new aftermarket body bushings at the same time.

 

[zildjian4life218]

You say explorer rear, what are the upper control arm mounts that are normally cast into the housing? What style upper arms are you running? Stock g body geometry? A swap kit with instant center relocation? Just adjustable mustang arms?

I will have to see if I can dig up some pics but it has a flat 3/16" plate that goes from each axle tube across the top and the UCA mounts are welded to it. I got a g body 9" bracket kit from ebay and trimed them to ft the 8.8 and welded them on. I am guessing they are taller than the factory ones. So maybe my IC is way off? Also I do not know if the lowers are further down or not. I guess that would also mess with the IC correct?

Just though of this too. If the car is lowered with springs will that push the IC further forward? These are the control arms http://umiperformance.com/catalog/index.php?main_page=product_info&cPath=8_60_74&products_id=94

 

[motorheadmike]

You are going to need to map it all out: driveline and suspension angles. Take the time and baseline the suspension and then move it into a neutral position, and change one thing at a time. If you want a constant start with your tires; and there is no reason to need bias ply over a good set of drag radials - yours are just very narrow and short. Don't make excuses.

KYBs are fine. I did a 1.7 on them with a 315/35R17 Nitto NT05R DR in my old Turbo Buick, 8 psi on the launch.

 

[zildjian4life218]

You are going to need to map it all out: driveline and suspension angles. Take the time and baseline the suspension and then move it into a neutral position, and change one thing at a time. If you want a constant start with your tires; and there is no reason to need bias ply over a good set of drag radials - yours are just very narrow and short. Don't make excuses.

KYBs are fine. I did a 1.7 on them with a 315/35R17 Nitto NT05R DR in my old Turbo Buick, 8 psi on the launch.

I will be getting slicks regardless. I grabbed the radials originally because I did not want to swap tires every time I got to the track. Well burning through a set of tires in 5000 miles was not fun so I now drive street tires to the track and swap on my radials. Radials are also shot. Down almost past the wear bars so I do not have much if any time left on them. So no reason for me to keep using the radials over slicks.
This weekend I can get the car up on ramps in all 4 corners and get under it and start getting angles for everything.
Is this a good list?

Driveline
Pinion
UCA driver and pass
LAC driver and pass
Pinion snubber room

What else should I get a measurement of?

 

[lilbowtie]

Here is an article you might want to look over. Your not spinning your roasting the tires w/ that 60 ft. You mentioned the radials are shot - big problem - I'm also thinking you have a miss match on your cam to rear end that at under 3500 it hooks and bogs the engine. 8 in of rubber isn't much, you can easily put a 9 in in there. A little more about your combo might help. trying to set up for street , road course, and drag is a challenge.
Google (Tuning 4 Link Rear Suspensions for the Drag Strip)

 

[zildjian4life218]

Here is an article you might want to look over. Your not spinning your roasting the tires w/ that 60 ft. You mentioned the radials are shot - big problem - I'm also thinking you have a miss match on your cam to rear end that at under 3500 it hooks and bogs the engine. 8 in of rubber isn't much, you can easily put a 9 in in there. A little more about your combo might help. trying to set up for street , road course, and drag is a challenge.
Google (Tuning 4 Link Rear Suspensions for the Drag Strip)

I understand there will be a level of compromise between the 3. I will mostly be street driving with the biweekly test and tune at the drag strip and maybe 1 or 2 road course events a year.

rear gear is a 4.30 and the cam is 231/236 @ 0.050" .641"/.615" lift on 111LSA. Compression is about 10.65:1. The cam manufacture Texas Speed and performance recommended the 4.30s over 4.10s to get it so the top of 4th I would be crossing the 1320' mark.

At the top of the track (1/4 mile) I am in 4th and maybe 6200-6300rpm. Redline is just under 7000.

 

[lilbowtie]

Great choice on the cam and gear, can't understand why it would bog. Are you running a carb? If I am guessing right your going through the traps at about 113mph. What are the numbers on the 1/4 mi run - guessing again your running 12.0's