60 foot problem with '86 firebird

casrak7 · 08-15-2016, 10:27 PM

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.

08-15-2016, 10:27 PM	#1
casrak7 Junior Member Join Date: Jul 2011 Posts: 63 Likes: 0 Liked 3 Times in 2 Posts	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.