What is this car trying to tell me?

[Ken01-Cobra]

Ok, I am more than a little perplexed by this car!

It has a dyno proven 304 RWHP, 300 RWTQ, C&L MAF, Steeda UD pulleys, Diablo chip, Bassani X w/cats, 2.5" Flowmaster catback, 4.30 gears, aluminum driveshaft, PHP brace and bushings, 2003 halfshafts, rebult rear end clutch packs with an extra friction plate, MM full length subs, Pro 5.0 shifter and the H&R 1" spacers on the rear.

Here's the deal...

With street tires and the 3.27 stock gears, I ran a best of 13.39@105+ mph.

After the changeover to the 4.30's, the car ran an average of 8.6x 1/8 mile times with street tires OR Nitto DR's. Weight was 3660 lbs. Street tire 60' was an average of 2.1. Nitto 60' was an average of 2.0.

Last Saturday at the track I finally got the chance to try the ET Streets and 15" Centerlines on the car. Weight was 3625. Conditions were brutal at 87 degrees and about 85% humidity. Elevation was about 500'. The track was hot and slick. I DID run a personal best of 13.25 on the first run. 60' was 1.88 on a 5 second burnout. ET's were set at 20 PSI. (yeah, I know they were high, but I planned to lower them as I went) 1/8 was 8.5x.

I thought maybe the C&L had taught the computer bad things, so I disconnected it for a half hour. No positive difference. Next run after that was a 13.4 with a 1.86 60' and 8.6x 1/8 and tire pressure at 18 PSI.

So it seems that SOMETHING is limiting this car. It SHOULD be capable of 12's. I am speed shifting the 1-2 and 3-4 shifts and doing a light lift on the 2-3, so I don't think it is shifting or the normal driver stuff.

If anyone has any ideas of what would cause this type of behavior, I would be very interested in hearing it! It's got me really scratching my head!

 

[SLOWBRA]

Ken,

That is semi-odd.. Last year with almost (No MAF) the same mods as you but I was at 290hp/299tq I was running 12.82's at 105-107 in the 1/4 with 1.7 - 1.8 60's on ET Streets.. 1/8's were around 8.0 and 8.1 at ~ 85-87 MPH.

I agee that something is limiting your car, I would try to run 13-15 PSI in the tires and be sure you are not hitting the rev-limiter on the 1-2 shift. I know it sounds odd, but my times were sucking because I kept spaking the rev. The 1-2, 2-3 shift I take all the way to 7 grand and the 3-4 I take to only like 6500-6600..

Do you have the dyno graph of the car in it's current shape?

Shawn

 

[Ken01-Cobra]

The last dyno on my Cobra page is with all current mods. The one dated 11/26/2002. Your numbers are more in the range I expect this car to run, but it just hasn't shown it's capable of it yet.

I shift at 6800 for the 1-2, 6900 for the 2-3 and 3-4. The 1-2 and 3-4 are speed shifts. I usually don't bounce off the limiter. I DO have a tendancy to bounce off the limiter in 2nd though. ;-) But even clean runs are nowhere close. The 13.25 was a clean run. The 2-3 shift was a bit slow, but not THAT bad! Still faster than most!

ONE run at an 1/8 mile track with ET Drags at 11 PSI the car ran an 8.1 eighth, but was squirrelly as he!! on the top end! Would this lead you to believe it might be a weight transfer thing? With the low pressure in the ET's, the car could squat and go? The 60' on that run was still only a 1.81.

 

[SLOWBRA]

To be honest, I am not familliar with the physics of how the tires work.. But I do know that I never hit 12's with them above 16 psi. 60's were all in the same range no matter if I had them at 13 or 18 psi.

11 psi would get a little scary (been there done that too), try 13 psi. I bet you can do it. With a 8.1 1/8th mile you will see your 12 sec slip!

 

[Ken01-Cobra]

Ok, I guess I will wait another 3.5 months for a decent weekend (e.g. no rain) and go back to the track and just try different launches and air pressures and see what happens. It just needs some scientific testing thrown at it I guess.

 

[99SVTcobraVERT]

why does your car weigh 3660lbs and its coupe???? my 01 convt on per weight at each wheel scale for a road race shop weighed mine in at 3610 with between 1/4 and 1/2 tank.... were you in the car? and even still you would have to be 300+ to turn a weight like that. keep in mind that i had bunch of crap in the car and it was with heavy chrome by 9inch wide rims and heavy soft compound 275-40 gforce KD. whats the deal??????

 

[Ken01-Cobra]

Hell, I don't know why it weighs that much! Yes, I was in the car! That is race weight at the track scale with 1/2 tank of gas, spare, jack, junk, trunk carpet, etc. removed. I don't weigh THAT much, but I am not a lightweight either @ 240 lbs. Last time, with the Centerlines and ET Streets vs. the Steeda Ultralites and Nittos, the car with me in it was 3625 in the above trim.

 

[Tim Lester]

I would try and put the stock mass air back on the car, you could even try that at the track the next time you go and see if there is a difference. Good luck Tim