Can't launch below 2.0 on DRs??

[z06resipsa]

I raced my 02 Z at the East Coast Corvette Show and Go at E-town yesterday to try out the new DRs I just purchased. Ran them at 22 lbs and left between 3000 and 3500 rpm with a slow pop. My best 60' was 2.004 and 3 of the 60's were under 2.1. I was not getting much wheelspin except when I left at 3500 rpm on one run, which resulted in a 2.147 60'. The car just didn't feel that strong coming out of the hole until the tach hits about 4000 rpm. It kind of bogs once the tires hook.

Also, when I started the car after my last time trial run, the check engine light came on so I didnt race again. I retrieved a "P0171 Fuel Trim System Lean bank 1-B" code. After starting the car three times, the check engine light went off. The only thing done to the car is a Vararam (no tune yet) that I installed last year. I've been to the track twice since installing the Vararam, and have not had any trouble before. I checked the intake for leaks, and found none. I did notice on the way home from the track, however, that the exhaust note seemed louder when I jump on it. But at idle and cruise it is the same and nothing is rattling. I pulled one the plugs and it looked normal (light brownish deposit), although the plug gap is slightly less (.057) than the .060 that GM specs them at (the car has about 9300 miles).

The track temp was 83 degrees yesterday and all my runs were between 12.450 and 12.633 @ hair over 114. Just for comparison, at the same event last year at E-town, the temp was 70 (according to the time slips) and I ran 12.398-12.533 with 2.15-2.22 60's on F1s and my trap speeds were 115.5+. I was leaving at about 2200 rpm last year.

What am I doing wrong, and is there something wrong with my car now?

[WA 2 FST]

If the car bogs at any point in time once the clock starts, you will hurt your trap speed. This goes for launch, and upshifts (which is why powershifting is the only way to wring out every last bit of ET _and_ MPH out of the car... I don't do it b/c I don't like breaking things 2+ hours from home).

The lean bank code is due to the Long Term Fuel Trims being out of range, but you have not "hurt" the car in any way. Oftentimes, just adding a cold-air intake will cause issues with the LTFTs, though, so a tune may be helpful for you to get all the power available in the motor as it sits currently.

You either need to roll into the throttle quicker, or launch at a higher rpm ... assuming you're getting some bog on launch.

[z06resipsa]

I got into the throttle immediately on the three runs i launched between 3000-3300 and got the bog. On the 3500 rpm launch, I got a significant amount of wheelspin and once the tires hooked, it still bogged. I've been looking at my average air fuel ratios that I have from a dyno that was performed on the car prior to the vararam install. My ratios are very lean at 3000 rpm according to my dyno sheet at 15.0. In fact, according to the sheet, my ratio is 17.0 at 2500 rpm. At the other end, my ratio drops to 11.2 or so at about 6000 rpm (its stays between about 14.0 and 12.8 between 3500 and 5,500). Probably the lean condition at the low revs is what's making the car bog with the DRs (notwithstanding the vararam which is really not doing anything in the 60'). I dont really know alot about this except Ive read that normally aspirated LS6s seem to make the most power at around 13.0.

I need to bring it to the dealer to take care of the ignition switch recall and to fix my broken electric window and door lock. Once the dealer has "fixed" my car (I look forward to that like a root canal), I plan to have it tuned.

[FRISKY]

It takes several burnouts and runs to get the slick mold release off new DRs.

M/T recommended air pressure:
P295 and larger sizes: 11 –14-psi
P275 and smaller sizes: 12 – 16-psi

Don't go below 11-psi starting pressure at the track and on the street/highway run 75% of the maximum pressure as noted on the sidewall of the tire. (About 30-psi) Don't go over 180-mph trap on DRs.

You should be able to launch 4000 – 6000-rpm if you use a soft clutch release.

Traction Control and Active Handling was off, right? Those A/F numbers were WAY off. Torque Management, Traction Control, Active Handling, high engine temperature or the lean air/fuel mix could be pulling the timing and/or fuel.

Expect 1.6 – 1.8sec 60’ times when everything is working properly.
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[z06resipsa]

Thanks for the info about the tires.

Those A/F numbers are what the dyno sheet say. The guy running the dyno stuck a probe in the exhaust pipe. I do not know whether this is an accurate method for measuring A/F but thats how it was performed and thats what the graph says. If it is accurate, those A/Fs are how the car came from the factory and before the Vararam install. The corrected rwhp was 359 on the first pull, 353 on the second pull and 333 on the third pull. No fan was used for cooling. The A/Fs got really rich on the third pull. The car's best run to that date was a 12.6 @118 at Atco with a 2.17 60' on F1s on a cool October evening. I always run in the Competition Mode.

[Dr.Ron]

I think your air pressure is too high. Go down to like 17psi cold. Don't forget the heat robs you of HP. You're releasing the clutch too fast or launching at too low RPM's if you're bogging. If you're spinning, you're most likely mashing the gas too quickly. A happy medium w/ clutch slip is what you need for a good launch, as well as a nice & smokey burnout.
Lower your psi, raise your launch rpm's & slip that clutch as you roll into the gas. I launched at 5000-5500 rpm's when I raced on DR's.
Ron

[tratr]

Your Vararam w/o a tune is definately hurting your trap speed. I have the trap and Kooks headers and my a/f @ 6000-6400 is 11.0 to 11.2. Some cars benefit more from a tune then others. In our case, it's definately necessary. I've purchased HPtuners and a wb and have the car running much better w/o the MAF sensor (12.5 to 13.0 afr in upper rpms). Still working on getting the MAF tune straight and have not been to the track but the car is definately stronger. Get a tune!

[z06resipsa]

Thanks everybody for the tips.