How to correct for Density Altitude (DA). Step inside.
10-01-2004, 10:47 PM
#1
Not DAVEB the parts guy
Thread Starter
Join Date: Aug 2000
Posts: 8,555
How to correct for Density Altitude (DA). Step inside.
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.
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.
10-04-2004, 02:50 PM
#5
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.
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.
10-05-2004, 05:40 PM
#7
Senior Member
Join Date: Apr 2003
Posts: 523
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 
10-06-2004, 06:31 AM
#8
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.
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.
10-07-2004, 03:21 PM
#10
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,
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,
10-07-2004, 03:27 PM
#11
Originally Posted by Mad-MAX_SE
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.
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...
9.065 at 79.67mph...time seems a little low, but since i beat a rather rich supercharged 2000SE max, it seems decently close,
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...
9.065 at 79.67mph...time seems a little low, but since i beat a rather rich supercharged 2000SE max, it seems decently close,
10-07-2004, 03:50 PM
#13
Originally Posted by Mad-MAX_SE
it may be that the altitude is wrong, but 5800ft is what i found searching for it....
10-07-2004, 05:04 PM
#15
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.)
10-07-2004, 05:34 PM
#16
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.
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.
10-12-2004, 09:23 PM
#22
Not DAVEB the parts guy
Thread Starter
Join Date: Aug 2000
Posts: 8,555
Originally Posted by BEJAY1
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.
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.
10-13-2004, 07:44 PM
#23
Originally Posted by Nealoc187
5800 foot elevation for a track in North Carolina? I think you better check that figure hehe.
http://americasroof.com/nc.html <- Highest point east of the Mississippi.
http://gorp.away.com/gorp/publishers...n/hik_ash2.htm
10-14-2004, 12:58 PM
#25
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
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
10-14-2004, 01:14 PM
#26
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.
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.
01-25-2009, 01:38 PM
#28
Member
Join Date: Oct 2006
Posts: 39
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.
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.
04-21-2012, 07:23 AM
#31
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...
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...
04-23-2012, 02:17 PM
#32
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...
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...
04-23-2012, 03:30 PM
#33
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
04-25-2012, 09:10 AM
#34
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!
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!
04-12-2014, 09:56 PM
#35
Supporting Maxima.org Member
iTrader: (16)
Join Date: Nov 2004
Location: Denver, Colorado
Posts: 2,761
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
01-25-2024, 08:46 PM
#36
Newbie - Just Registered
Join Date: Jan 2024
Posts: 1
Much confused.
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+
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+
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.
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.
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