How do I find the DA? It's not on the timeslip or the track's website. I know the altitude is 600' above sea level. I know the air temp was approx. 65 degrees. Can DA be calculated? If so, what are the variables that I need to know to calculate it?

Its a pretty complex calculation with vapor pressures and humidity and other stuff. I have one in excel I'll post tomorrow. I think it only requires temperature, altitude and humidity. After a night at the track I go to wunderground.com to find the humidity.

I get DA from my weather station. There are a couple of problems with calculating it. The first is getting accurate, up to date weather condition readings. Conditions can change in an instant. Another problem is the formula. While there may be a scientifically correct formula, the different weather station manufacturers often use their own. Autotronics, the manufacturer of the Performaire that I use say that they use a proprietary formula that is better suited to how a race care reacts to weather conditions. The bottom line is if you are going to use the DA as a factor in putting a number on the window, make sure you use the same instruments or weather station all the time. Even weather stations of the same brand can vary.

RACE ON!!!

I forget where I got these calcs from, but it determines everything from RH, barometric pressure (inHg), and OSA temperature (F). (OSA=outside air)

It's in excel. I won't even try to spell it out here, it's uses about 5 different equations.

Maybe one of you with a weather station or a different formula can compare it and see.

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CFI is right, the # really is all of the place, in part depending on who you talk to in what part of the country..... and what pressure you use. With the handheld stations such as Tag's, they're also sensitive to where you keep'em..... in the sun, it'll read high, in the shade, maybe too low. Important thing is consistency if you're a bracket racer.... they are changing their dials based upon what the DA is.... it better be acurate, or they're a 1st round runner-up.

Regardless, with the DA, I believe it consists of 4 different elements 1) Actual elevation 2) Temperature 3) barometric pressure 4) humidity

Actual elevation and Temperature will effect DA by far the most..... barometric pressure and humidity also have effect it, but not nearly to the extent that the other two will have..... in otherwords if you race on top of a mountain in 100 degree heat.... you're hosed :sad5: and you can expect to see losses in et that range from a few tenths to as much as a full second literally..... damn mountains are evil !! :evil3:

Actually physical altitude reading isn't part of the equation. The thinner air at higher altitudes results in lower barometric pressure. The barometer reading automatically factors in the altitude. Where I race the barometer never gets higher than 25" hg. A "standard" barometer at mean sea level is 29.92" hg.

I couldn't compare my weather station with the calculations of someone else, unless we were side by side. I don't have a way to input the numbers for it to calculate. It reads the conditions and reports both the conditions and the DA simultaneously. I believe there are some systems that have instruments that take readings and gives you a calculator and a formula. The Tag and the Performaire systems figure it directly then report the results.

RACE ON!!!

Thanks for the info guys! I'm not going to be bracket racing but really always wanted to know where the DA number came from and what it's importance is. Now I know!

So... what is zero DA?

Obviously it's at sea level. But what temperature and humidity?

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I guess I should check in more often. Zero DA doesn't have to be at sea level any more than 5000' DA has to be at 5000' altitude. Zero, or sea level DA occurs when the barometer reads 29.92" HG absolute, at 60° F, and 0% humidity.

RACE ON!!!

Here's the easy way to do it. Click on the link below; choose the track, date, & time of the pass, and voilà... you now have the DA. It may not be as accurate as having your own weather station, but it's a lot easier.

Dragtimes DA calculator

Wow, that calculator just picked me up a tenth and a half! HAHA!

Cool calculator, thanks for the link.

According to that, the DA was 1803 when I ran.

Calculator shows a corrected run of 10.532 @ 132.841 mph.

Actual run was a 10.66 @ 131.08.



Next time out I'm going to run an actual run of 10.47 @ 132.5. I'll post it up and let you know if I'm a good guesser or not.

Thought I'd follow up since I stated what I'd run next time out. I did go again as many of you know by now, ran an actual 10.55 @ 132.78. Broke my rear and bottle pressure was down. New rear with lower gears and another bottle heater for next year. I'll be shooting for a 10.30 @ 135. Might be a stretch but it will be fun to try!

REALLY hoping for a 11.9X on motor in the spring. I'm close now at a 12.08. Hopefully the 3.45's will get me there.

Still considering water/meth injection with the nitrous, but I have no idea how much that will help the timeslip I'm guessing a couple tenths, but it will be a while before I'll know the answer to that.

For corrected timeslips and DA (since DA is what I started this thread for), my 10.55 run, corrected, would be a 10.50 @ 133.52. DA was 1090.

Those are still some awesome times, corrected or not!

Matthew