Cobra running slower

[jdogg43]

Ok so I took my car to the track Friday night and ran a PB of 11.20 @115 with a 1.53 60ft. The next day my car wouldn't do any faster than 11.80's at 110. With the six speed the fastest I ever went was 12.20 @ 119, I know that going auto slows down the trap speed a little but can't figure out what's going on.

Also it was slightly warmer Saturday compared to Friday night and da went from -1000 to 3000 but I didn't know it would slow me down so much? Cars seems to run fine just slower.

Mods:
2.8 upper only
Off road x pipe
C4 auto with 3000 stall
Sra with 3.73
Slicks and skinnies

 

[cobracide]

Datalog if you really are serious about finding out what is going on.

 

[jdogg43]

I ran the hand held data log, timing was same both nights (20 degrees) A/F was lean but not sure how accurate my sensor is because I have a slight exhaust leak before sensor. It was showing 12.5

 

[04cobra3]

Well to the best of my knowledge every 1000 feet in da you either lose or gain a tenth and the oat makes a huge difference so with temperature in mind and with the da theres a drop of roughly 4 tenths so those could be legit numbers pending on how much of a temperature difference there was. Just my two cents

 

[DSGCOBRA03]

It, could be the da, but I also lost 5 mph only on the back 1/8 of the 1/4 when my intercooler pump failed. My 1/8 mile time was the same. You could compare your slips and see if it's throughout the whole 1/4 or just the back 1/8. My car was also running just a 2.8 upper.

 

[jdogg43]

It was through the whole pass, 60ft was a whole tenth off as well, and I dead hooked evey pass.

110 mph just seems really slow to me, I run 115mph at a local track consistently. Just seems weird to run so much slower all of the sudden and nothing seems to be wrong


I've been told that with my ET being low 11's I should be in the 120+ mph

 

[matt87]

intercooler pump take a dive?

 

[jdogg43]

Hmm something I can take a look at.

 

[matt87]

any finds?

 

[badcobra]

Belt slip. Check for excessive rubber where the supercharger belt rides.

 

[jdogg43]

Haven't had a chance to get out in the garage, I have a compression checker too so I'm gonna do that then check intercooler pump.

When is the intercooler pump come on? Is it at a certain temp?

 

[jdogg43]

I watched my boost gauge during very last pass and it held steady at 11 psi all the way down the track

 

[jdogg43]

Compression is good 148-150 on all cylinders, intercooler pump came on right when I started car. At least it was swirling in the tank