Also posted this on YB and getting a lot of looks but not much info...

Looking for advice as to whether my suspension is leaving some ET on the table or not.

1991 firebird with a 406, 11.8:1 comp with old AFR 210's not-ported, mini-ram and solid roller cam 248/248 625/625 on a 110, TH350 with ATI 8" 4500 stall, Strange 12-bolt rear with 4.56's , 28x10 Hoosiers in rear.

Currently running 17psi in the slicks, -2 angle on the torque arm, lca brackets in the lowest hole and mid setting on the qa1 rear shocks set at mid point. Front struts are 90/10 lake woods. Rear suspension is all spohn chromoly with spherical rod end and a drag bar preloaded. Springs are Eibach Drag Launch springs

Car weighs 3565 with driver and gas. Last week it went a best of 11.15 @ 121.4 with a 1.55 60' time.

Doesn't feel like it's spinning but looking for advice on how to lower the 60' time a little.

Launching by foot braking the car. I bring the idle up a little so it not choppy (2000 ish) and then stab it the last yellow.

Thanks for any/all responses.

Picture of launch



Video of launch

http://vid52.photobucket.com/albums/...ps1q4k4ymq.mp4

 

Looks like it is leaving well . especially for foot breaking. Have you tried letting a little more air out of the back slicks or playing with the settings on the rear shock ?
Whatever changes you make, do it one at a time and back up the pass.

 

That was the first time to the track after throwing the kitchen sink at it (changing everything in rear suspension) so I have not tried any variables yet.

If I change the shock settings, would I go looser or tighter? Also I could try going lower in air pressure, that is good idea to try.

Ultimately I think the car needs to be lighter. I am looking into a racecraft k-member/a-arm/coil over kit. I like the idea of rack steering but do not want to lower the car any more than it is. This couples with Strange drag brakes should shed a few pounds off the front end.

 

Yep, that's a nice looking launch.....

My setup is similar to yours. I built some travel limiters on my car to keep the front end down, and that helped lower my 60ft times and kept them more consistent. However my car is lighter @ 3200lb race weight.

 

Heat seeker, how much travel do you limit the front suspension to?

Also how did you make your car so light? 3200 is with you in it? Wow.

 

I believe the normal travel is about 6" total. I limit mine to about 2-3" depending on the track prep.

Yep, with me in it. Here's some of my weight reduction:

Passenger and back seats removed.
Fiberglass spoiler & hood
Front and rear bumper supports removed.
HVAC is gutted from behind the dash.
Front sway bar removed
No engine accessorizes or brackets
No power steering (manual box)
Electric water pump
Re-moveable wiper motor
Battery in the rear (weight transfer)


You get the idea.....

 

I still have the stock formula hood but was considering a fiberglass one. I have read varying results on the weight savings though. bolt on hood should weigh around 25 lbs and stock one one should weigh 50-75 lbs.

How involved was the front and rear bumper supports? Did you reinforce with anything or just take the crashbar out?

I have to do the HVAC from behind the dash yet.. That will be a winter project.

I already deleted my front sway bar, power steering, A/C, serp brackets and water pump. I also have the CSR alumnium water pump and only an alternator left. Also put the battery in the trunk.

Sounds like we have very similar setups.

 

I dont think you will get much improvement in the suspension at this point. Focus on taking away antisquat if you can maintain traction. Other than that, you are still leaving pretty easy. Need to leave with more rpm and stuff to start taxing the suspension.
Or spray it. Lol

 

Lighter never hurts but I was trying to think of things you could try they will not cost you any money.
I would defiantly let some air out of the back tires first. Maybe a couple pounds at a time and see if there is any improvement in your 60. Do it until it falls off then go back a couple pounds. Most guys with your setup run around 10 or 12. but every car is a little different. I have seen guys run 8 with no problem. Once you feel you have hit the sweet spot then try to lower the back shocks one click at a time. If that does not help you can try going up . Don't think you are going to go to far either way.


The car already launches very well.
If you are going to put some money it and your class allows it a trans brake would be they way to go. Then you can advantage of your 4500 stall.
There are several ways to go after your goals, just some thoughts.

 

I would put radials on it and run 20+ psi.

 

If you're not spinning, it doesn't look like you have excessive antisquat and the front isn't lifting too much (you're not wasting a lot of power getting the suspension to work)I don't think that there is much that you're going to do to the suspension/tires to run a faster 60'.

I'd be focusing on tuning and trying to make more power (maybe mess with timing in that range...) till you start having traction problems or too much suspension reaction and then start messing with the suspension again.

 

Sometimes with smaller slicks more air pressure can help gain et. try to go up as far as u can until it spins then go 1lb lower. remember this is not 100% thing but worth a shot. you could be wasting power planting the tire harder than needed. remember it is heavier car and needs more forward force to move it long as its hooked it doesn't need to squat more per say to leave right.

 

we had a street strip 89 rs car original v6 car had factory suspension aka wore out bushings etc. 388 pump gas motor made 425 hp 472 tq went best 1/8th mile 7.24 1.50 60' only weight reduction was no back seat and no jack lighter wheels manual steer no extras under the hood jus alternator electric water pump still had crash bars front and rear battery still in front. 4.10 gear with mini spool. so sometimes its finding the right combo that works and drive the wheels off it and collect win lights.

 

I have one if your interested, a Twin Turbo fiberglass hood, just needs some icing here and there, then paint. I'm right next door in Old Bridge...

 

Street Lethal, appreciate the offer but the next revision of the motor (which is in the planning stages now) may require an EFI converted Super Vic intake which would require me going to a 4" cowl hood. I was thinking about doing the hood before the motor because of the weight.

 

Oh it'll fit...

 

Just the one pic ya have..its hard to tell. But you do have better weight transfer then a lot of guys on here with rattle trap race cars...(all cut up)...when you hit it off the line and hook.ya want the car to push forward..not skip...and part of the push..wheels will lift..footbraking is a blast.with a good convertr.

Watching the video.
I would not go under 15psi in the slicks...(18 to 20psi)
can you get the rpm/converter up in the 3000 rpm ballpark and then flash it.