unexpected results, colder mat = slower

[ashford]

ive been trying to help a friend get his car to run a low 10 second pass. the car is a 93 mustang, stock 5.3, beefed 4l80 with trans brake. the car has a air to water intercooler with radiator.

it ran a best of 10.43@133 and worst of 10.67@128 on one day racing( my car ran a best of 9.37 that day for reference). mat temps were north of 200* at the end of a run. so for the next race we installed another air to water in series with the other one with an icebox in the trunk. the next outing weather was perfect for a turbo car track prep was ideal. my car ran a 9.14@153 without being touched from the last day out.

his run on the other hand was a 10.7@127 with mat @ 85* at the end of the run. boost was near the same as last time out but a bit rich, i pulled a bit of fuel and made another pass. he ran a 10.59@130. i looked at the log and saw iat at 125 at the end of the run and he said he accidentally turned off the intercooler pump when he turned on the launch after the burnout.
the next run was a 10.67@128 with mat at 87*
just to verify the next run was without the pump on it was a 10.62@129 with mat at 128*.

i find this very backwards from expectations. does anyone have an explination for this? like perhaps it needs to be leaned out a bit, combusion effeciency declines with dropping temps.

[slow_hemi6]

Anyways I would like to know the 60' for the runs before I made any conclusions.

[slow_hemi6]

Ashford?

[Dennis_Zx7r]

Maybe the MAT correction doesn't fit the vehicle. This seems to be quite a big change in temp, which means theres quite a drastic change in fueling with the base MAT curve.
Do you have logs from both runs?

[ashford]

i havent been able to get ahold of the time slips my friend has been out of town this week but if memory serves me there was no outstanding difference in 60 foot time the car has a consistant 1.54-1.59.

yep the mat correction was a bit off on the first pass(no pump) it had afr from 10.1-10.8 i was able to pull fuel in the fat spots but the next pass with the pump on injectors went stactic and had the jump to rich at the top of 3rd gear but the resulting afr was in the ok range yet at 10.2.

it might be an e85 thing i don't know

[slow_hemi6]

Ok so a few issues here. The MPH for your runs should be producing faster 1/4 ET than you are. You have a traction issue for sure. Also those 60' are also off as you can get a 1.45 60' and a 10.43 with 127mph. Once again sounds like your spinning in the 60". Very hard to make consistent runs if you have traction issues. ET is never a good indicator of power. MPH is the best indicator of power for tuning purposes.

[Rick Finsta]

Agree - I hit high 1.5X 60's and my car is a full second slower and runs out the quarter around 112-114mph. Look to the chassis for this one.