ok so i have a 2004 RCSB 5.3L silverado 4x4. two weeks ago i ran a 15.77 @ 86mph. all i had on the truck then was a free-flowing exhaust. since then i've added an intake and a westers tune. went to the track tonight. first pass was 15.28 @ 90mph with a .22 reaction time. not bad. half second off. well, my second, third, and fourth passes went like this, respectively: 15.39, 15.38, 15.48. all of them with the same basic reaction time (.22 give or take a couple hundreths). i'm kind of disappointed. i would have been happy if i had stayed around 15.2 or gone a little lower, but worse? also i was pretty much the same exact weight as i was when i ran the 15.7 a couple weeks ago. i'm just worried something's not right with the tune or something causing me to get worse times. any ideas? also, how much will my times drop with the addition of long tubes?

 

Changes in atmospheric conditions could easily account for one or two tenths. Were you keeping notes?

 

weather changes or if you were hot lapping those slower runs, the truck might have been getting hot.

also... idk if you know this or not, but i couldnt tell from how you were explaining yourself... but reaction times dont contribute to the final time, its just for if you are racing someone.

 

oh yeah, you're right about reaction times. so scratch what i said about them.

the weather didnt seem to change at all. it was overcast and kind of cold. low 60s to high 50s. there was a chance of rain all night so maybe i could see atmospheric changes. i just didnt think it could affect a car/truck that much.

and as far as hot lapping, my truck wasnt hot at all. one pass it was a little cold i think. some ricer decided to destroy his head gasket and spill coolant all over the track, so we had a long wait. but each time i ran, with the exception of one, it was the same temperature roughly.

maybe i just need to go out and spend some money on performance parts.

 

good idea

 

The weather plays a huge part. Be it the humidity, more is better, cool air vs. warm, pressure density ect...

 

alright. i'll blame it on the weather. makes me feel better. haha thanks fellas.

either way though, i need to spend more money on this thing. long tubes are next. then maybe e-fans. depends on how much money i want to save for college.

 

It's completely the weather, A long time ago I went from running 14.50s in warm weather to 13.90s in a little bit cooler weather.

 

yeah. it's weird though. all 4 of the passes were made within 2 hours. didnt think the weather changed much but i guess so. either way, my best was a 15.28. that's still way too slow, regardless of weather or anything.

 

It is best to calculate the Density Altitude each day ( I do it by the Hour ) and correct to standard.... that way you can tell if your mods are doing you any good... and it is best to go by MPH... you power can go up but your ET can be worse due to spinning from extra power.. here is a link to the calculators:
http://www.modulardepot.com/?show=resources
and a good weather info link.
http://www.wunderground.com/