Morning, I know how us Mopar racers like to share all our tips and knowledge so please help me out here....

So this was my first weekend of tracking weather run to run and calculating the DA and Relative Density... I bought a weather station that tells me temp, humidity%, and pressure in inHg... I’m using the calculator at Dragtimes.com to get the DA and Relative Density.... I can access the site from my phone which is handy enough and I’m charting everything in a excel spread sheet... I think I will play with it and try to put the formula into the spreadsheet and phase out the phone... anyway...

I would like someone to explain how they set the pressure at the track... If you drive 2 hrs from your house to the track and there are multiple elevation changes, wont that throw off your base barometric pressure reading???

I am looking for some feedback from bracket racers that chart weather changes over the weekends and how the changes affect your car. I can only assume that every car reacts a little differently. I also want to know what is “good” and “bad” air.... how your cars react to change in DA and Rel. Density....

The truck is a naturally aspirated 440... We’ve had some issues but we’ve only run in what people are saying is “bad” air....

Here are some readings I have some Saturday and Sunday... I’m going to leave out the ET’s because I was making changes to squirters and timing so that would move things around. Sunday I never took the hood off but I lifted early in elimination so the numbers are off a bit.. basically ran 11.06 to 11.15 over 7 runs over 2 days...

Track elevation =630 ft

2:32pm Saturday – Temp=74, Bar press=29.86, Humd=67%, Calculated Da=2039 ft, Rel. Denisty=94.17% (Good, Average, Bad)???

7:54pm Saturday – Temp=69, Bar press=29.86, Humd=67%, Calculated Da=1705 ft, Rel. Denisty=95.11% (Good, Average, Bad)???

1:46pm Sunday – Temp=80, Bar press=29.88, Humd=64%, Calculated Da=2456 ft, Rel. Denisty=93.01% (Good, Average, Bad)???

3:04pm Sunday – Temp=84, Bar press=29.90, Humd=57%, Calculated Da=2685 ft, Rel. Denisty=92.38% (Good, Average, Bad)???

I’ve done a bit of reading about this.. I understand as the altitude increased the air is less dense and that’s a bad thing.... I would really like to know some bence marks as to what would be good, bad, terrible air and how much your guys cars fluctuate with changes.

Thanks a lot for helping!!!

ET on a gasoline vehicle will probably have about a .01 per 200 ft DA change, methanol half that.
DA is a function more of oxygen available rather than true elevation by barometer readings. Humidity is factored in to give a good reading that will track with performance. Find out what your racer changes per .01 et versus DA, keeping a close eye on wind. After you have established a base line of runs, go back and look at conditions that can affect overall ET, like different 60 fts. You can then pin it down better. I look a segment times as well, from the 60 ft to 330, or 660. 1/8th mile ETs are better to establish a baseline with, more consistent on average than 1/4 mile ETs. You can then use a run completer, if need be. Also be aware of track temp, cloudy Vs sunny (track temp again).