How true is Density Altitude and drag racing?
08-18-2010, 12:17 PM
#1
How true is Density Altitude and drag racing? Im having a little doubt in this da thing. Im not saying its totaly fake but im questioning if its as big a deal as people say. Ill give you the reasons why with stats and maybe someone can educate me.
My info and stats...from 8/6/10
DA was 2062...best run on street tires...13.087
Stats and info from 8/11/10
The things that were different from the track passes this time was I got rid of 40lbs,I used my et street radials (which is .4 diameter taller),and the Freakin DA was 601 lower!
DA was 1461...best was 13.074
What gives man? 601 less da,40lbs less weight,drs,and could only get .013 lower.
One thing I have thought about is the diameter of the drs are .4 bigger than the street tire diameter. Yea I know,everyone SAYS its not that big of difference but how much we talkin? Just enough to sneak in 12.999? Any thoughts or ideas of what it could be?
Maybe ill have to take a run up there today and do first couple passes with street tires then switch to the drs to actually see what that .4 difference in diameter really is? I know its something sso small and stupid but I do have a point and you have to give that to me.
My info and stats...from 8/6/10
DA was 2062...best run on street tires...13.087
Stats and info from 8/11/10
The things that were different from the track passes this time was I got rid of 40lbs,I used my et street radials (which is .4 diameter taller),and the Freakin DA was 601 lower!
DA was 1461...best was 13.074
What gives man? 601 less da,40lbs less weight,drs,and could only get .013 lower.
One thing I have thought about is the diameter of the drs are .4 bigger than the street tire diameter. Yea I know,everyone SAYS its not that big of difference but how much we talkin? Just enough to sneak in 12.999? Any thoughts or ideas of what it could be?
Maybe ill have to take a run up there today and do first couple passes with street tires then switch to the drs to actually see what that .4 difference in diameter really is? I know its something sso small and stupid but I do have a point and you have to give that to me.
Last edited by senicalj4579; 08-20-2010 at 11:47 AM.
08-18-2010, 12:57 PM
#4
#1 You need to provide all the data for those runs.
#2 Air Temperature plays a fact as well as Temp in the pavement part of the track too.
Wiki actually has a good explaination....
http://en.wikipedia.org/wiki/Density_altitude
Both an increase in temperature and humidity (to a much lesser degree) will cause a reduction in air density. Thus, in hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.
The power output of the engine — power output depends on oxygen intake, so the engine output is reduced as the equivalent "dry air" density decreases and produces even less power as moisture displaces oxygen in more humid conditions
Meaning that you basically have less oxygen molecues give a specific amount of space/volume and your engine will only be so efficent in packing in that air. You need to know the other weather related info to add to the DA # that Lebenon Valley puts at the bottom of the time slip.
I am willing to wager conditions were different, you may have had a tail wind the first time and a head wind the 2nd, humidty may have gone up, temp may have varied or LVD' DA calc is off.
MOST time real race cars have tools to figure that out but on Wednesday night they generally are not there, on Sat and Sun they show up with the equipment.
DA is a accurate tool for generally understanding the conditions in which a race occured, I kinda associate it with a SAE correction that Dynos use to adjust for current weather conditions and locations to compare HP/TQ to other cars across the world.
Long story made short.
You run your car at the hottest, nastiest time of the year at LVD, and then take the exact same car, drive to Atco or E-town on one of their coldest days DA-2000 track rental days.
IF with in reason you do the same 60' you will pick up between 2-4 tenths of a second guarrenteed.
You will notice if your here long enough, some of the guys with fast cars do not start running them until it gets VERY cold to put up new PB. Guys in Denver and other logistically high alt places call BS but still their cars will run faster when they get to a good track like Atco/E-town.
#2 Air Temperature plays a fact as well as Temp in the pavement part of the track too.
Wiki actually has a good explaination....
http://en.wikipedia.org/wiki/Density_altitude
Both an increase in temperature and humidity (to a much lesser degree) will cause a reduction in air density. Thus, in hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.
The power output of the engine — power output depends on oxygen intake, so the engine output is reduced as the equivalent "dry air" density decreases and produces even less power as moisture displaces oxygen in more humid conditions
Meaning that you basically have less oxygen molecues give a specific amount of space/volume and your engine will only be so efficent in packing in that air. You need to know the other weather related info to add to the DA # that Lebenon Valley puts at the bottom of the time slip.
I am willing to wager conditions were different, you may have had a tail wind the first time and a head wind the 2nd, humidty may have gone up, temp may have varied or LVD' DA calc is off.
MOST time real race cars have tools to figure that out but on Wednesday night they generally are not there, on Sat and Sun they show up with the equipment.
DA is a accurate tool for generally understanding the conditions in which a race occured, I kinda associate it with a SAE correction that Dynos use to adjust for current weather conditions and locations to compare HP/TQ to other cars across the world.
Long story made short.
You run your car at the hottest, nastiest time of the year at LVD, and then take the exact same car, drive to Atco or E-town on one of their coldest days DA-2000 track rental days.
IF with in reason you do the same 60' you will pick up between 2-4 tenths of a second guarrenteed.
You will notice if your here long enough, some of the guys with fast cars do not start running them until it gets VERY cold to put up new PB. Guys in Denver and other logistically high alt places call BS but still their cars will run faster when they get to a good track like Atco/E-town.
08-18-2010, 01:56 PM
#7
#1 You need to provide all the data for those runs.
#2 Air Temperature plays a fact as well as Temp in the pavement part of the track too.
Wiki actually has a good explaination....
http://en.wikipedia.org/wiki/Density_altitude
Both an increase in temperature and humidity (to a much lesser degree) will cause a reduction in air density. Thus, in hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.
The power output of the engine — power output depends on oxygen intake, so the engine output is reduced as the equivalent "dry air" density decreases and produces even less power as moisture displaces oxygen in more humid conditions
Meaning that you basically have less oxygen molecues give a specific amount of space/volume and your engine will only be so efficent in packing in that air. You need to know the other weather related info to add to the DA # that Lebenon Valley puts at the bottom of the time slip.
I am willing to wager conditions were different, you may have had a tail wind the first time and a head wind the 2nd, humidty may have gone up, temp may have varied or LVD' DA calc is off.
MOST time real race cars have tools to figure that out but on Wednesday night they generally are not there, on Sat and Sun they show up with the equipment.
DA is a accurate tool for generally understanding the conditions in which a race occured, I kinda associate it with a SAE correction that Dynos use to adjust for current weather conditions and locations to compare HP/TQ to other cars across the world.
Long story made short.
You run your car at the hottest, nastiest time of the year at LVD, and then take the exact same car, drive to Atco or E-town on one of their coldest days DA-2000 track rental days.
IF with in reason you do the same 60' you will pick up between 2-4 tenths of a second guarrenteed.
You will notice if your here long enough, some of the guys with fast cars do not start running them until it gets VERY cold to put up new PB. Guys in Denver and other logistically high alt places call BS but still their cars will run faster when they get to a good track like Atco/E-town.
#2 Air Temperature plays a fact as well as Temp in the pavement part of the track too.
Wiki actually has a good explaination....
http://en.wikipedia.org/wiki/Density_altitude
Both an increase in temperature and humidity (to a much lesser degree) will cause a reduction in air density. Thus, in hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.
The power output of the engine — power output depends on oxygen intake, so the engine output is reduced as the equivalent "dry air" density decreases and produces even less power as moisture displaces oxygen in more humid conditions
Meaning that you basically have less oxygen molecues give a specific amount of space/volume and your engine will only be so efficent in packing in that air. You need to know the other weather related info to add to the DA # that Lebenon Valley puts at the bottom of the time slip.
I am willing to wager conditions were different, you may have had a tail wind the first time and a head wind the 2nd, humidty may have gone up, temp may have varied or LVD' DA calc is off.
MOST time real race cars have tools to figure that out but on Wednesday night they generally are not there, on Sat and Sun they show up with the equipment.
DA is a accurate tool for generally understanding the conditions in which a race occured, I kinda associate it with a SAE correction that Dynos use to adjust for current weather conditions and locations to compare HP/TQ to other cars across the world.
Long story made short.
You run your car at the hottest, nastiest time of the year at LVD, and then take the exact same car, drive to Atco or E-town on one of their coldest days DA-2000 track rental days.
IF with in reason you do the same 60' you will pick up between 2-4 tenths of a second guarrenteed.
You will notice if your here long enough, some of the guys with fast cars do not start running them until it gets VERY cold to put up new PB. Guys in Denver and other logistically high alt places call BS but still their cars will run faster when they get to a good track like Atco/E-town.
Iv never been to LVD only NED. Iv heard NED is worse as far as track prep and DA seems to always be a little higher at NED. What do you say?
Last edited by senicalj4579; 08-18-2010 at 02:02 PM.
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08-18-2010, 02:00 PM
#8
I also am only getting the DA calulations from http://www.dragtimes.com/blog/densit...-da-calculator
Idk how accurate it really is.
Idk how accurate it really is.
08-18-2010, 02:33 PM
#9
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I told you this in your last thread. You're pissing in the wind. You aren't even datalogging what your car is doing. You can not have repeatability when your PCM is constantly adjusting. Get a GOOD tune first, then worry about variables such as DA. Also, take some pressure out of those ET Streets. 30 is WAYYYY too much. You may not feel like it's slipping, but they probably are. Have a friend take a video of your passes and make sure you're repeating everything the same way every time. Same burnout, same groove, put your pants on the same way every day.
08-18-2010, 02:40 PM
#10
I told you this in your last thread. You're pissing in the wind. You aren't even datalogging what your car is doing. You can not have repeatability when your PCM is constantly adjusting. Get a GOOD tune first, then worry about variables such as DA. Also, take some pressure out of those ET Streets. 30 is WAYYYY too much. You may not feel like it's slipping, but they probably are. Have a friend take a video of your passes and make sure you're repeating everything the same way every time. Same burnout, same groove, put your pants on the same way every day.
08-18-2010, 04:03 PM
#13
I really didnt spin any on 30 psi. But like dirty said...the spinning was probly minimal.
08-18-2010, 05:49 PM
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To the OP, you do not have near enough data to determine how DA is affecting your runs. There are so many factors that affect your times, without logging tons of runs, you can't make an accurate assumption.
08-18-2010, 09:18 PM
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As a bracket racer for 18 years, I can tell you weather conditions play a big factor! I've mentioned this before, as have others, but DA is more than just a calculation. You have to look at what the temperature, humidity, dewpoint, barometer, wind and track temperature are, plus your car's vitals if you want to seriously crunch the numbers. Jeg's and Summit both have great log books, and you might find using one helps you understand and make more sense of it all. I keep 1-3 years of records with me at the track, and when going through runs I can tell if the car is running right, what dial-in to use for eliminations, and so on. I also use a Kestral weather meter, and you might find a weather station of some sort AT THE TRACK will give better information than the nearest airport (not a bad source of information, but unless it's very close, there will likely be variances).
Derek
Derek