60 foot problem with '86 firebird
 

started out:
86 firebird. STARTING OUT : 2,850 race weight. Stock style suspension (aftermarket torque arm in lowest position at front mount), adj. lower control arms (in lowest position on rear housing side). th350 w NO T-brake. 5000 converter. 28x10.5 slicks (std. sidewall). 4.56 geared 12 bolt. Lakewood 70/30 struts. 14"/175# front coil over springs, with 4" of upward strut travel possible. Strange double adjustable rear shocks set in the middle for rebound and compression. Under slow motion viewing, the rear wheelwell shows NO separation and only 3/4" of squat.
First trip out - 60 footed a 1.51, 10.37 best with 134.5 mph. 104.1 mph at the eighth. Trans eventually broke after testing a few days later.
Second trip out - discovered that while footbraking with the th350, the front rubber brake lines that went to the calipers were collapsed and not releasing until about a full three or four seconds after the pedal was let go. It explained the lack of eighth mile mph.
Installed a 1.80 Powerglide WITH T-brake, and "different brand" 5000 converter. Best time was 1.48 sixty foot, 107.5 mph at the eighth, and a 10.24 at 134.5. Tried several two step chips between 3500-4500 without change. Had noticably a rotation or two of wheelspin. No rear shock adjustment helped the 60 foot.
Third trip out - Put in an A-1 brand 6200 converter. Also realized the front end was VERY hard to budge when lifting on it manually. It had a 14"/175# springs, we changed to 14"/225# and it got much easier to lift. We then tried a 12"/325# spring and it got better yet. BUT STILL VERY STIFF in comparison to most other cars Ive seen. Could maybe use a 12"/400# spring. In going with the shorter spring, The strut's upward travel now had 5 1/2 possible. Like this the car went a 1.45 best 60 ft. 107.5 mph again in the eighth. And ran two 10.14s, followed by a 10.15 at a better 136.8 mph. The A1 converter definitely seems to be efficient upstairs. We again tried sevaral two step chips ranging from 4500-5500 to no avail. Car is crossing at 7700 rpm which is near perfect for us because we dont want to spin this budget shortblock over 7800-8000.
But with all this mph, and knowing several friends with similar combinations......the sixty foot is still way off. We have freinds with near identical weight and tire sized cars going mid 1.30s in the 9.85-9.95 range at 133 mph. They use converters in the 5600-6200 range like ours. Why does ours feel soft? The power is absolutely there. We were told front suspension limiters would help out the sixty foot as long as the car is hooking. Thankyou for any and all suggestions. Frustrated.
p.s.
engine power - 604hp@7000, 521 ft lbs at 5400-5500.
385 sbc, rev/max 230cc import heads Carbide only ported. 2.08/1.60. 13-1 compression, Holley strip dominator intake, Quick Fuel 950 carb, camshaft is 256/263 @ .050 .690/.660 on a 107 lsa , 103 i.c.

Re: 60 foot problem with '86 firebird
 

Buy & read the "The Doorslamer Book" and it will answer ALL of your questions including "instant center" and the stored energy of the front springs.........

This isn't a one answer fix, but it is a way to learn how to set up your racecar......

Re: 60 foot problem with '86 firebird
 

'89 Camaro

Depending on which motor we have in it, our best in the 1/4 is 9.42. You're mph is better due to the rear ratio, we run mostly 1/8 stuff so have it geared up with a 5:14 in a 9" Ford. Convertor is about 6100 from TSI, Powerglide is 1.80.

The front of the car is really basic for us. We put in a set of Moroso springs 10 years ago and whacked two coils off for ride height adjustment. We still use the OEM struts - had about 85k on them when we got the car. Changed it to a Vega box and removed the sway bar.

At the rear, we have the stock rear springs, aftermarket torque arm, UMI lower control arm brackets (top hole) and a S&W rear sway bar deal to stop the twisting motion of the car. 8 point cage and frame connectors of course.

60 foot is usually in the low 1.30's - the UMI brackets and the rear sway bar made the biggest impressions on the ST.

So I think you're wasting too much time on the front end and the car sounds like it might have a lot of wasted motion in it, which of course leads to higher ST's and ET's. It also has the IC sitting too far in front of the car, ideally it should be about where the engine/trans come together. Lowering the rear of the lower control arms will move the IC closer to that spot and really help the car move on the launch.:)

Re: 60 foot problem with '86 firebird
 

One thing that you might want to consider is the instant center. On a torque arm car the IC is directly below the front mount of the torque arm. That is, if your rear lower control arms are not pointed at a radical angle. They should be pretty much in line with your sub-frame connectors. Pointing your lower control arms at the center of the torque arm moves the IC to that point. It will give the feel that you are hitting the tires hard, but you are actually putting the rear suspension in a bind. Another thing to note is that torque arm cars do not like to squat.

Re: 60 foot problem with '86 firebird
 

As it sits.... the rear lower control arms are in the lowest position on the rear mount. But they are not at a radical angle. .... they are still basically parallel to the ground. So as far as i can tell. ... the ic is as far back as it could technically be? On a slow motion video which is extremely clear and close up. .... the tire doesn't spin..... at least not for the first fifteen feet of camera view. There is about 3/4" of body separation on the initial hit. Should we try to limit this body movement by counteracting it with a stiffer rebound setting on the rear shock? And if that sixties better. .... then move to the front and start limiting travel to take wasted motion out of the front until it spins? Is a tenth in just wasted motion plausible?

Re: 60 foot problem with '86 firebird
 

Can you post a photo of your rear suspension?

Re: 60 foot problem with '86 firebird
 

slow motion video of the 1.45 sixty....

http://vid1315.photobucket.com/album...psvxspazq3.mp4

Re: 60 foot problem with '86 firebird
 

Just to hammer a little bit on what I said previously - or as they say a picture is worth a thousand words...

www.rutherfordms.com

There is a picture of our Camaro leaving the line on the main page (4th flash pic) with the modifications that I mentioned previously.

Seriously if the lower bars are basically parallel with the frame connectors then your IC is out there in front of you - way out there. The car will never work any better. What you have is decent, the slight body separation, planting the tires looks good - it's just not quick.

Re: 60 foot problem with '86 firebird
 

LOL!

http://i85.photobucket.com/albums/k5...Wheelstand.jpg

Re: 60 foot problem with '86 firebird
 

so......Even if its NOT spinning.....we could be down a tenth in sixty foot?