Explain DA, & optimum weather for drag racing?
05-20-2002, 09:43 AM
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Re: Explain DA, & optimum weather for drag racing? Bob and Greg can explain this alot better than I can I'm sure, but I'll take a stab.
Density altitude ( for our purposes ), is basically a means for describing how the weather conditions are going to effect our engines performance.
Look at it this way, if you enclose a 1 foot glass cube at sea level, in that cubic foot volume of air there is going to be so much oxygen. If you do the same thing on the top of mount everest there will be less oxygen in the air. Why would that be? air has 21% oxygen. well the air on mount everest is ,much less dense (less tightly packed), thus there is less molecules of oxygen in that cubic foot volume of air.
What effects density altitude?
Barometric pressure. Think of the atmosphere as a land mass...some places it is high, some places it is low. if you take your glass square and stretch it to the top of the atmosphere..if the atmosphere is significantly higher...there is more gas molecules pressing down, thus the pressure is higher, and the density is higher. if you go up in altitude...the column of air above you is decreased in height...so your actual barometric pressure measured right where you are at is less. ( thats why you shouldn't use sea level corrected BP's in calculating the DA ).
Temperature.
Guess as temp goes up the molecules get more active, and the gases expand some, so less oxygen molecules per volume measurment.
Humidity.
Water is a contaminant! it displaces potential air molecules.
Basically the DA formula takes the wetaher conditions, and then gives you a number that says. your current weather conditions are the equivilant to xxxft altitude in a standardized column of air.
the lower the DA the better!
Barometric pressure...the higher the better
Temperature...the lower the better ( offset by problems with track hooking when temp gets too low)
Humidity...the lower the better.
When you calculate DA correctly you should not correct for altitude, if you use the station pressure at the track...your actual track altitude is reflected in that.
**** I can even spell meteor(blah)(blah) , so take it with a grain of salt <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
Density altitude ( for our purposes ), is basically a means for describing how the weather conditions are going to effect our engines performance.
Look at it this way, if you enclose a 1 foot glass cube at sea level, in that cubic foot volume of air there is going to be so much oxygen. If you do the same thing on the top of mount everest there will be less oxygen in the air. Why would that be? air has 21% oxygen. well the air on mount everest is ,much less dense (less tightly packed), thus there is less molecules of oxygen in that cubic foot volume of air.
What effects density altitude?
Barometric pressure. Think of the atmosphere as a land mass...some places it is high, some places it is low. if you take your glass square and stretch it to the top of the atmosphere..if the atmosphere is significantly higher...there is more gas molecules pressing down, thus the pressure is higher, and the density is higher. if you go up in altitude...the column of air above you is decreased in height...so your actual barometric pressure measured right where you are at is less. ( thats why you shouldn't use sea level corrected BP's in calculating the DA ).
Temperature.
Guess as temp goes up the molecules get more active, and the gases expand some, so less oxygen molecules per volume measurment.
Humidity.
Water is a contaminant! it displaces potential air molecules.
Basically the DA formula takes the wetaher conditions, and then gives you a number that says. your current weather conditions are the equivilant to xxxft altitude in a standardized column of air.
the lower the DA the better!
Barometric pressure...the higher the better
Temperature...the lower the better ( offset by problems with track hooking when temp gets too low)
Humidity...the lower the better.
When you calculate DA correctly you should not correct for altitude, if you use the station pressure at the track...your actual track altitude is reflected in that.
**** I can even spell meteor(blah)(blah) , so take it with a grain of salt <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
05-20-2002, 11:18 AM
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Re: Explain DA, & optimum weather for drag racing? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Black Sunshine/ 00SS:
<strong>In detailed, laymans terms. What is good, what is bad, what is the best.. Etc. Thanks.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">As long as you can hook, i.e., track not too cold, you want cold air, high pressure, and low humidity, at the lowest altitude track possible. You can hope for a downsloping track and a tailwind, too, while you are at it, but they don't affect DA.
<strong>In detailed, laymans terms. What is good, what is bad, what is the best.. Etc. Thanks.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">As long as you can hook, i.e., track not too cold, you want cold air, high pressure, and low humidity, at the lowest altitude track possible. You can hope for a downsloping track and a tailwind, too, while you are at it, but they don't affect DA.
05-20-2002, 01:53 PM
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Re: Explain DA, & optimum weather for drag racing? Yes, yes, yes, and yes. LOL.
DA (density altitude) is a number that is referenced to what the World Meteorological Organization (WMO) refers to as a 'standard atmosphere at sea level'. That standard atmosphere is at follows:
Temp 59F (15C)
Hum 0% (dry air - never occurs naturally)
Baro 29.92 in/hg (1013.2 mb)
Those conditions would give you a DA of 0 ft...ie...sea level.
Increasing temperature increases DA.
Increasing humidity increases DA.
Increasing Barometric pressure decreases DA.
The inverse of each, of course, will result in....uh...well...the inverse of each. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
There is no 'best DA'. The lower the DA, the more power you will make. Of course, really good DA's are most often associated with cold weather, which might preclude good track conditions, but you get the idea.
Tracks that are physically at or near sea level will have an advantage of those that are hundreds - or thousands - of feet above sea level, simply because they have more atmosheric weight (measured as barometric pressure) pressing down on them. So places like Atco, E-town, VMP, MIR, HRP, most Florida tracks, etc, have an advantage over most other tracks when the weather gets cold.
I think the other guys had already explained it pretty well, but I hope that adds just a bit more info. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
Bob
DA (density altitude) is a number that is referenced to what the World Meteorological Organization (WMO) refers to as a 'standard atmosphere at sea level'. That standard atmosphere is at follows:
Temp 59F (15C)
Hum 0% (dry air - never occurs naturally)
Baro 29.92 in/hg (1013.2 mb)
Those conditions would give you a DA of 0 ft...ie...sea level.
Increasing temperature increases DA.
Increasing humidity increases DA.
Increasing Barometric pressure decreases DA.
The inverse of each, of course, will result in....uh...well...the inverse of each. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
There is no 'best DA'. The lower the DA, the more power you will make. Of course, really good DA's are most often associated with cold weather, which might preclude good track conditions, but you get the idea.
Tracks that are physically at or near sea level will have an advantage of those that are hundreds - or thousands - of feet above sea level, simply because they have more atmosheric weight (measured as barometric pressure) pressing down on them. So places like Atco, E-town, VMP, MIR, HRP, most Florida tracks, etc, have an advantage over most other tracks when the weather gets cold.
I think the other guys had already explained it pretty well, but I hope that adds just a bit more info. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
Bob
05-20-2002, 11:02 PM
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Re: Explain DA, & optimum weather for drag racing? What we need is a track located by the Dead Sea on a 50 degree day. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
The Dead Sea is something like 1,200 ft below sea level, I believe.
The Dead Sea is something like 1,200 ft below sea level, I believe.
05-21-2002, 01:54 PM
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Re: Explain DA, & optimum weather for drag racing? Thanks everyone, that about explains it.. <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />
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05-21-2002, 02:05 PM
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Re: Explain DA, & optimum weather for drag racing? Bob Cosby - or anyone else.. What affect would each increment of, say, 500 ft of DA have on ET's? In other words, if I ran a 12.00 @ 1000 ft., what would that be @ -1000 ft? Or 500 ft to 2500 ft? Any ideas? If someone has figured that out it sure would be helpful. Or, would it be different for each application/car?
I've done too much to my car over the last year to know what the DA is doing for me.
I've done too much to my car over the last year to know what the DA is doing for me.
06-11-2017, 03:16 PM
#9
Wow, I'm going to necro bump a 15 yo thread to answer the question above. I was researching the subject matter and came across this thread. The answer to the question above can be found at the following link...
http://www.biondoracing.com/tips.shtml#WS
http://www.biondoracing.com/tips.shtml#WS
06-11-2017, 03:46 PM
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Wow.. I was a senior in high school when this thread was made.. I'm going on 32 now 
