Have you ever been to the track and heard a gearhead say, "Damn the DA is crappy today!" and you think to yourself what the hell is DA? DA stands for Density Altitude and it's the way drag racers correct thier times to compensate for weather conditions and altitude. Changes in weather and altitude can play a huge role in how your car performs. Keep in mind that some tracks are just plain faster/slower than others thanks to differences in timing equipment, the grade of the track, track surface, and the way MPH is calculated.

Here's how to start:

1) Find out the elevation of your track. Use a good search engine and you should be able to find it.

2) Go to www.wunderground.com and find the city where your track is. Once you've located your area, you can dig up historic weather conditions for any day in the past 10 years. You'll want to get the temp, baro pressure, and dew point of the time and date of your run.

3) Go to http://wahiduddin.net/calc/calc_hp_dp.htm and input your numbers. Hit the calculate button and locate the calculated Density Altitude. The DA number generated is the calculated theoretical altitude during you run.

4) Take your DA number and apply to the NHRA correction factors table http://www.gnttype.org/techarea/misc/altitude.html

5) Calculate your numbers and that is what your car should have run under ideal conditions. Sometimes your DA actually shows NEGATIVE altitude which means the car is performing far better than normal and there's nothing to correct and compensate for. Usually only coastal areas in the South, East Coast, and Northeast will experience these rare conditions thanks to low altitude and strong high pressure areas due to the proximity of the ocean (~400 miles). It's also a primary reason most of the "freak" cars reside in these regions.

Here's my favorite corrected DA:

August 20, 2003
96 degrees
32% humidity
29.89 baro
62 degree dew point
950 altitude
DA 3800'

Actual ET/MPH: 14.65@94 2.23 60'
Corrected ET/MPH: 13.98@98mph

On average, my DAs show my car should technically be in the 13.9-14.0@99mph+ range with 2.2 60 foots. However, until I run 13.9-14.0, my car will remain a 14.4 second car.

Calculating for DA is great in that it lets you gauge your cars performance during the season and between the tracks, but for the love of God do not use it was justification that your car is quicker than some other guys. You run what you run. If anything just state that the DA you ran in was really poor and people understand. Correcting your slips and putting it your sig is as bad as using G-tech numbers.

 

Good stuff Dave

 

My DA on the day of my PB was -1129
The DA on Wed when I ran was 383

 

-1129 feet lol dead sea dragway

 

Crap! Those are some good conditions.

My personal best was run on a day that had a 1200 ft above sea level air density.

I once ran in -490 ft when I ran years ago in NC. I am capable of running 14.2s, if I can just get an DA of around -500 ft.

 

I'm glad this was brought up. Angers me when there are people asking why they ran a 16.xx when they're 5000'+ above sea level and have a reasonable amount of mods.

 

The only other minor thing to consider is the situation in which a time with a positive DA is converted to the lower time at sea level. Would the driver have been a good enough driver to deal with the extra power (traction) if they actually were at sea level? Correcting times = fun

 

Corrected times are more useful in determining whether or not a car is making the power it should from the trapspeeds. Cars are much more consistent than drivers in most cases.

Dealing with the power shouldn't really be an issue I don't think as were only talking about fluctuations on the order of 5%, maybe 10% in very extreme cases.

 

You mean traction problems? What's that? I never hear my tires chirp off the line.

 

wow...i inputed all my info and calculated the DA for my best time recently which was a paltry 10.128 at 71.63mph at Dunn-Benson Dragway, NC. I was shocked that i went up almost .7 from my last outing.

Temp: 75.2
Baro: 30.07
Dew Point: 69.8
Altitude: 5800ft

The DA was an astounding 8338ft!! Using the calculator from the nhra website, which by the way didn't measure that high, lol, i extrapolated the numbers for 8300 ft...times go down by .0013 per 100ft, traps go up .0014 per 100ft...

9.065 at 79.67mph...time seems a little low, but since i beat a rather rich supercharged 2000SE max, it seems decently close,

 

I don't see how the track in NC can be that high of DA. Crunch the numbers again and see what you come up with. It has to be over 145 degrees for you to get those kind of numbers.

 

it may be that the altitude is wrong, but 5800ft is what i found searching for it....

 

I don't think the mountains of NC get that high is most places. When I searched for the city of Dunn, NC; I am getting around 200 ft elevation.

 

5800 foot elevation for a track in North Carolina? I think you better check that figure hehe.

 

I just typed in dunn-benson dragway elevation in google and found what I think you were looking at... 5800 feet. But that was for Bandimere dragway in Colorado. It was just on the same page as dunn benson was (it was a page of grand prix 1/4 mile times.)

 

lol, i guess i should have clicked the link, at 200ft it's a DA of 1447ft...now time to recalculate....

9.96 at 72.85mph....that's seems better.

i was runing consisten 9.5-9.6 at 74-75mph at rockingham in the 1/8th with my 16's and 225/50 16 sumitomo htr+'s. now i have 18's with 245/40 18 BFG Geforce TA KDW's, which are over an inch in diameter taller than the 16" wheel tire combo.

 

i hate numbers. my DA turned out to be 598 and that isn't even close to the numbers on the NHRA correction factors table. i dunno maybe its just becuase i'm tired? :dunno:

 

your et correction factor is .9952 and you mph correction factor is 1.0045

 

so my corrected time is 14.19 @ 96.44 mph. I'll have to see if I can't better this corrected time next time out.

 

Good info Dave. Makes me feel better. My PB was a DA of 2367 plus a headwind of 20mph. Like Mike said, I need to get out again.

 

nice thread

 

Headwinds are strange things. I've run in some pretty strong wind 10-25mph and you'll agree anything over 15mph is downright gusty. My timeslips show a very slight decrease in ET, but my MPH goes to crap. The day I ran in 20mph+ headwinds, my traps were down well over 3mph and my ETs were done just under .1. I guess on the last 1/8 mile is where the wind really robs your power.

I've seen it work the other way too. When I ran my 99.51mph trapspeed, I had a nice 15mph tailwind.

 

Yeah to my knowledge there are no dragways in the Appalachian Mountains.

http://americasroof.com/nc.html <- Highest point east of the Mississippi.

http://gorp.away.com/gorp/publishers...n/hik_ash2.htm

 

gimme a break guys....i made a mistake, lol. even neal saw what i did...but i still had a decently high DA for my recent runs...

 

Rockingham Dragway
Elevation: 375ft ASL
DA after running through those tables: 1275ft
Mean Temp: 66
Dew Point: 45
Baro: 29.73

thats if someone wants to double check to make sure I did this right.

ET that night: 13.90@100.87

Corrected using NHRA table using 1300ft: 13.70@102.31

Rockingham has brand new lighting and timing equipment so according to these tables I can do better

 

Did this for another day when I ran my PB 13.63 and it gave me a DA of 1146ft...

Using 1200ft

13.63@101.05 = 13.45@102.35 pretty accurate from my other day. 13.6 was on slicks and the 13.9 above was on street tires. I guess my car has its good days.

 

Dang, why isn't this thread a sticky?

EDIT: Thank you.

 

Intersting post. There are no correction factors close to the calculated 8150ft DA I calculated for my 14.858 @ 93.28 run at Bandimere. Heck, Bandimere's actual elevation is 5880 and the chart doesn't even go that high.

If I use the NHRA's factors for Bandimere on an ideal day, that calculates out to a 13.78 @ 100.4 mph.

http://www.nhra.com/content/about.as...601&zoneid=101

My 10.99 @ 134.44 in my Mirage calculates out to a 10.19 @ 144.83 mph, though this was using the same calculations, boosted cars should use half calculations.

 

thats pretty cool info!! didnt know what DA meant either cause i havent been to the tracks in a long time..

GOOD LOOKING OUT!!

 

v nice that is a big diffrent

goood job

 

There's so much more to just hitting the tracks and running your car. Aaron has been schooling me on it. Racing is science, just wish he could of explained it to me face to face though He does know his stuff.

I'm slowly getting it and i'll have him to thank for it when I hit a 14 flat or possibly a 13.99 in the max...

 

Thanks. People usually don't realize that having good weather conditions at the track can really make a huge difference.

 

Yup, typical DA's for my local track are in the 7000-8000 range, so I suppose I'd be happy if I ran a 14.5 locally.

After I get my battery tied down, I hope to try this track thing out for the first time.

http://www.airdensityonline.com/trac...4.417847305013

 

About the worst DA I've ever experienced was just over 5000' in Las Vegas (2000' elevation) in 100 degree weather. It was nice when I moved to NC and I shaved almost a full second when racing on a cold day at a sea level track.

I remember I use to post my 1/4 mile times on this forum and people would say that my car is slow when it ran a 16.7 with just a cheap cone filter. I had to explain that I was in higher elevation. But if I was at a sea level track, I would have been in the low 16s, which is pretty good for an almost bone stock 92 Maxima SE VE30DE Automatic. That same car is now running 12 flat NA. Ahhh, the joys of modding a 4 door grocery getter!

 

Yeah it's so weird one day I break out and run my fastest time ever No rhyme or reason in my mind but I bet I just had a good DA that day.

I run at Bandimere when I do,
http://www.bandimere.com/services/trackFacts.php
Basics

1/4 mile drag strip
Track Direction - South to North
Elevation - 5800' above sea level (5280 is a mile)
Sanctioned by the NHRA
Radio Frequency - 95.1 FM
Host over 125 events each year
Established in 1958 by John Bandimere, Sr.


Found this DA table for Bandimere: http://www.airdensityonline.com/trac...4.014520008019

 

How the h*ll is this possible? If it takes you 1320 feet to get to 76 mph. How are you doing it in 9.96 seconds????

im no mathematician, but if you can only reach 76mph in 1320 feet, I don’t see how you could do it in <10 seconds.

Every sub 10 car I know is trapping 140+

 

You reply to a nearly 20 year old thread post and can't understand that there are 1/8 mile tracks?