Problem cutting a light
 

I have a 93 Formula f body firebird I run In D/PS.I am having trouble cutting a light with the car. I shallow stage, rpms at 1500 at start. I leave as the last yellow is starting to come on and the car gives me a .671 light. I made a second pass to make sure it wasn't me, it was another .6719. I have been fighting this all year. I have put air bags in the rear with 25psi in right rear, 5 in drivers. I have tried 35psi to 10 psi and no difference. Lower control arms are level with the frame ties. I have tried lowering them and it seems to hit tires harder. The torque arm is in the stock setting, but not mounted to the trans. Springs are v6 springs with a 1/2 coil cut off. The rear shocks are 50/50 new lakewood. Stock anti roll bar. I have 145#s of weight in the rear of the car to make weight. The converter is built for the car combination. I have 4.56 rear gears with 26x8.5 rear tires.
The front suspension has 6" of travel for the front tires to fall out of wheel well. Lakewood 90/10 shocks with stock springs on front with 1 coil cut off. I was thinking of making front end limiters so i could make the car move forward. In the car, it seems like the car is trying to rock back on the rear tires, while lifting the front. The 60ft times are great. Here are my times

1.608 60ft
8.10 1/8th
82.56 1/8th mph
12.82 1/4
102.89 1/4 mph

I run 22 psi in the rear tires. The 60s are very consistent, and the car runs dead on the money every pass. Ran two 8.102 Saturday in tt and dialed in a 8.09. Ran 8.10 1st rd and lost because i had a .6719 light. I practice on a practice tree every night. I am very consistent on it in several different situations.

I am going to lower the torque arm 1 1/4 inches in the front and see what happens. Is that the right move ? Also how many racers use front end limiters on there stockers? Is 6" to much travel? Was thinking of limiting to 4" and see what happens. I am looking to classracer for help. Thanks In advance.

Re: Problem cutting a light
 

It's a good sign if you're consistent. But is there another carb you could try? Could you have a carb "flat spot" that's not very obvious? Converter might be at least part of it, but that's still a lot to be "off".

Re: Problem cutting a light
 

It's a fuel injected car. It could possibly be converter. I ordered this one from mark yacovone . I have never tried another converter in it.

Re: Problem cutting a light
 

Whats the launch rpm?

Re: Problem cutting a light
 

Starting line rpms are 1500. I've tried 2000, but 60s slowed down and didn't seem to improve lights.

Re: Problem cutting a light
 

I'm not familiar with FI cars, but I suppose it could still have a "flat spot" at the hit if the fuel curve isn't correct. Kind of like having an accelerator pump squirter that is way off on size and/or duration.

Off hand, I can't imagine a converter affecting RT's that much.

As an experiment, perhaps you can compare yourself to someone else in another car or practice tree to see how much of a variable you might be. Just trying to cover all the bases.

Re: Problem cutting a light
 

Joe, How high can you foot brake it to? I can't imagine a higher starting line RPM not affecting r/t.
Being a Pure Stocker with limited duration, it may indeed go faster leaving at a low RPM.
You might end up with an eliminator setting and a different one for qualifying ..Not unheard of.

Re: Problem cutting a light
 

The last thing to leave the line is the front wheels...start limiting all the wasted motion that the car goes through........too much front end travel......not enough air in slicks ect....even consider solid body bushings...

Re: Problem cutting a light
 

How much air in the front? With 26" it would take a large change in air pressure to affect rollout. Also, how high can you make the rear tires? Lastly, you sound consistant at the tree. Try (in testing of course), bumping in deeper on the line. Two runs only bumping once, then two runs bumping twice etc. It is worth a shot.

Re: Problem cutting a light
 

You might want to try a taller rear tire. I believe the class allows a 29.5" x 9".

Re: Problem cutting a light
 

All these ideas are great.

Mark, the harder I leave on the starting line, the harder the car lifts the front and hits the rear tire. When the front of the car lifts more, the slower the car reacts. The converter works great. I cannot see it being that because of how consistent it is.

Gump,
I have thought about taller tires for the rear. I have non to try at the moment.

I have 50psi in the front tires trying to make them the least amount of contact with the ground. They are 165/70/r15 volkswagon tires. Not race front runners.

I have tried bumping in 2 bumps at the line. It kills the et and made the lights drop to .590- .600 range.

As far as the efi having a flat spot. I have tried another chip in the ecm from another tuner and it slowed the car down and the reaction got slower.

I Have cut some .530 lights with the car, but I was anticipating the light.

All these Ideas are great. What about torque arm angle? Do I have too much front end travel? Thanks AAron

Re: Problem cutting a light
 

Cheap way out: Leave at a different spot on the tree?

Re: Problem cutting a light
 

Front end travel is usually a very big amount of change in RT.....

It is in a first generation F-Body....and more than a tenth is up there in those cars.

Maybe not as much in a later model with coil over type front end....

The problem is always limiting travel at some point will hurt weight transfer and traction....

Shorter front tires.....less front end travel....raise your starting line rpm as much as possible......

What do you want good RT's or the fastest ET's....One does not go with the other in a car like this......that's why people deep staged.....Speeds up RT's but kills ET's....

Re: Problem cutting a light
 

A friend just had a VW radial come apart on him this past weekend, almost flipped car. His were pretty new, i took my old ones off and I'm glad I did
You want shorter front tires for a faster reaction time and less rollout..
I've had RT woes and biggest improvement i saw once I worked tuneup and suspension was converter. Your RT are quite a way from fine tuning something if they're in the .6's. It does sound like a stumble or delay in the engine to be that late.
My 3rd gen has a lot of frt. end travel but I can still get it to react good .

Re: Problem cutting a light
 

What gear do you have in the rear end?

Re: Problem cutting a light
 

Part of the reaction time equation is your vehicles rolling resistance (RR). The less (RR) the faster the car will move from a dead stop. Try increasing the rear tire pressures in 1 pound increments to see if that helps with your RT. If it does, keep increasing the tire pressure until the improvement stops or you get tire spin. Because of your consistancy with your reaction times in the .671 area, I don't think you have a converter issue either.

On another note what rear tire do you run? I am not familiar with P/S rules regarding tires. Your 60 foot time seem a bit slow. I run 1.60 60 foot times but our car weighs almost 4300 lbs with driver. My guess you are at around 3,500 lbs. You get this RT issue straightened out, you are going to have a killer vehicle/driver combo. Good Luck.

Re: Problem cutting a light
 

have you ever driven another car? 670 is out to lunch I would be 570 in a slow car had to deep stage would be 520 then?

Re: Problem cutting a light
 

The car weighs 3680. I used to race super street for 20 years. Then took a break in 2008 and just returned to racing the beginning of this year. I will try the rear tire air pressure this wed. Rear gear is a 4.56.

Re: Problem cutting a light
 

I would think some more gear would help. That's a heavy ride. Are you still trying to drive this car on the street. I would think a 5.13 would be better

Re: Problem cutting a light
 

Is there any play in the ends of or slack in the throttle cable?

Re: Problem cutting a light
 

No street driving. Engine has no power above 5250 rpm and I go through at 5500 in 1/4 mile. Thats with a 4 spd automatic. Every one has given me some great ideas. Thanks for the help.

I don't know about the slack in the cable. But maybe I need to mess with the eccentric the cable sits in. The gas pedal has alot of travel also. Any body else have any expierence with a slow moving accelerator pedal?

Re: Problem cutting a light
 

There were a lot of good suggestions on this thread. Let us know if anything helps.

Also, a 4.56 gear seems a bit short. I would think a taller gear in the 5.00/5.13 range would help also. I think that small block of yours would like a taller gear.

Re: Problem cutting a light
 

This is a Pure Stocker. In this form the LT1 makes power to about 5200. It doesn't need more gear. In fact, I think it would do way better with the taller tire that I suggested.

A few years back, I built a Stocker using a stock LT1 with some High School kids doing the work. It eventually ran 7.05 in the 1/8th mile!

Re: Problem cutting a light
 

Out of curiosity, what were your 60 foot times?

Re: Problem cutting a light
 

Our best was a 1.41.

Re: Problem cutting a light
 

My LT-1 Stocker ran pretty fast with a 4.56 gear.

I changed it to a 4.88 and it did not go faster. Just pushed the rpm up.

One of the best runs I ever made was shifting out of low gear a good 1000rpm lower than normal. The car went up in the air pretty high and I was manually shifting it.......just pushed the shifter before the shift light went on.......

60' times were down in the lower 1.30's back then in good air...

Re: Problem cutting a light
 

It may like a steeper gear, if the transmission will make a WOT 3-4 shift. Sounds like you go though the traps in third gear. This would give you more starting line ratio, which might help your reaction time.

If you are still using the stock ECM, make sure you raise or disable the MPH limit .

Re: Problem cutting a light
 

It Goes through the traps in 4th gear. Rich you may be on to something. I let the transmission shift itself for the 1-2 shift. I think the trans may be shifting as the front of the car is raising from the higher stall speed.As in, as soon as I hit the throttle on the starting line, it shifts gears because of the WOT shift points with the stock governor are 4500 rpm. I put that governor in there because It likes to get out of first gear ASAP. I did not think it would shift that fast though. I am going to try and shift it manually out of first gear and see if that helps. Sounds like this is self-inflicted....... Thanks Guys, I will let you all know how it works.

Re: Problem cutting a light
 

Some factory stock ECMs will retard timing when going to the floor off the line. Also on the shifts.
Ed Wright could tell you more about this.

Re: Problem cutting a light
 

Fix this and the car will pick up a bunch.

I am assuming that you are still running the stock cam?

Re: Problem cutting a light
 

If it was shifting automatically at 4500....

What does the converter flash stall up to on the launch?

If it is higher than 4500.....there's your problem...

My LT-1 Stocker converter from Dynamic flashed to 5200-5300....

Footbrake launch at 3000 is about as high as you can go and be green with 26-27" front tires and full travel....

That's a very hard leaving stocker......1.29 was it's best 60'

Re: Problem cutting a light
 

Finally got my junk out to try some of your methods to cut a better light. What I did was shifted manually from 1 to 2, Moved the seat forward 1" at 2000 rpm , and that gave me a .088 light.

Then I bumped in 1 bump on next pass and it gave me a -.024 and killed my et 05 at 2000 rpms .

So for 1st rd, I bumped in shallow and left at 1500 rpms and gave me an .058 light.

With that being said, I tried leaving harder at 2000 rpm, It killed my 60ft to a 1.68.
As soon as I dropped it back down to 1500, I was back in the 1.625.

When I leave it in 2nd for it to auto shift, It gives me bad lights, but a 1.603 60s. Guess I cant have it all.

So now I have a qualifying run procedure and a elimination run procedure. Thanks for all the help. Aaron