LuvC5s

I have this in a different thread but thought it be best to start a new one. So I took my car to the track last night and got in 4 passes. Last week my best 60' was a 1.77 but I missed third on that run and the next I did a 1.80 60', 7.274@ 100.28 at the 1/8, 9.344@ 1000' and the car went 11.109 at 129.05

Here is my dilemma, last night I went 1.702 60' launching around 4000rpm, in the 1/8 i went 7.245 @ 98.23, and 9.383@ 1000' and ET of 11.19@ 125.68.

Next pass and best I was launching at 4000 and slightly rising while riding the clutch.
60' - 1.671
1/8 - 7.174 @ 98.13
1000'- 9.322
ET- 11.154 @ 123.89

The car seemed to be lacking the pull from 3 to 4 and 4th on. The only thing I did to the car since then was changed my catch can to a MightMouse PCV can and it is hooked up correctly. Why could be causing me to lose MPH!?? I figured with that last pass I should have been into the 10's. I am wondering if something is hurt on the car, NEED opinions or help!?

smokinstorm

Was the DA the same on both outings?

LuvC5s

I'm not sure. I think it got cooler this past time out but humidity was like 70-75%, dew points were around 63 and temperature was 71 degrees. Remind me again what the DA is? I'm having a brain fart.

smokinstorm

Density Altitude is a measurement of how dense, therefore how much oxygen is available in the air. It's a measure of relative density of the air measured in feet above or below sea level. It takes into account the elevation of the track, temperature, relative humidity and barometric pressure. Every thousand feet one way or the other is worth approximately .1 and 1 MPH. That's just a general rule and your results may vary somewhat. That's why you typically run .2-.3 tenths quicker and 2-3 more MPH in late November vs mid July. The DA might explain away some of your performance loss but you seem to have lost more MPH than what just bad air would explain away.

LuvC5s

I'll have to remember to look into recording that data next time. I don't have a weather station so how can you find out what the DA is that day? Weather Channels/Online?

smokinstorm

http://dragtimes.com/da-density-altitude-calculator.php

HOXXOH

If you want a rough estimate based on the closest airport. However for more accurate info online go to weatherunderground.com and find the weather station closest to the track. Then go to Google Earth to find track elevation. If you want to chart progress, plug the numbers in the Dragtimes calculator to get the sea level adjustment.

BTW, the OP's problem is on the back half, since his 1/8th ET increases in line with the 60'.

LuvC5s

I'll look more isn't the DA next time out. I was told I may be having some belt slip issues which would make more sense for the drop off in ET and MPH. I didn't notice any signs of belt slip but I could be wrong. Any ever have issues with belt slip and correcting it? I have a 6rib belt. Julio at Cartek told me to really consider buying a flip drive to eliminate it.

GARY2004Z06

Great answer.
Much better than Dragtimes.

383vett

Did the wind pick up later in the day? 5 mph is a big difference. Just have to take it out again next week.