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Old 05-20-2019, 05:36 PM   #1
Maroon 6.2L SS
 
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Density Altitude and E.T results

Hey all. I just recently learned a lot about Density Altitude. I went to the strip yesterday and a major storm front was coming in. Right before the front was coming in the DA was 2170'. Right now the DA at the same track is 580' and still dropping and will probably continue to drop into tomorrow.

I ran my worst run right before the storm at 2.08 60' and 13.28 E.T
Back in early April, I ran my best at 1.89 60' and 12.72 E.T
(no changes in the car setup)

Is it normal to see this kind of change in 60' and E.T with a significant change in DA?

I did read a post about a guy that ran a 10.40 E.T in one state and 11.60 E.T in another state and commented about the DA change. That's HUGE!!!
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Old 05-20-2019, 08:22 PM   #2
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Drag Time App can educate you if you play with it awhile. It will correct a time to sea level.
It has weather history for most drag strips. You can see what the DA was in April and what it was yesterday and compare to see how much the weather affected your runs.
DA is mostly determined by the temperature. Cooler air equals lower DA.
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Old 05-20-2019, 10:16 PM   #3
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DA is a combination of temperature, humidity and barometric pressure.


Lower temperature means there is more oxygen per unit of air, lower humidity means less water per unit of air, higher (or rising) barometric pressure means more oxygen per unit of air.


Perfect storm of DA is lower air temperature, lower humidity and rising barometric pressure. A combination of all three results in the most available oxygen per unit of air. More oxygen in the air results in better performance by the engine.
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Old 05-21-2019, 07:18 AM   #4
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DA changes have a huge impact on MPH and ET all other things remaining the same (Track, Prep, Wind direction). I have seen a .4 sec and 4 MPH change in 1 week down here in Florida going from -1000 to +2000 DA in a 4400 lb CTSV.

Similar results in a 4100 lb ZL1. On average .1 sec and 1 MPH difference for every 700-1000 ft change in DA over the past 10 years in racing in Florida with all Rides in Sig below.
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Old 05-21-2019, 06:34 PM   #5
Maroon 6.2L SS
 
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Thanks everyone. Everything makes sense now. I looked over my time slips from now back to early April. The dragtimes app helps for sure. My best was around 400 DA and my worst around 2400 DA.

I did notice something though!!! I had three runs on a test/tune day that were around 150 DA and my times weren't quite as good as my times with the DA around 400. I think everything was pretty equal. Might have been me or the track though, not sure.

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Old 05-21-2019, 08:13 PM   #6
Joe M 2012 2SS

 
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Quote:
Originally Posted by Maroon 6.2L SS View Post
Thanks everyone. Everything makes sense now. I looked over my time slips from now back to early April. The dragtimes app helps for sure. My best was around 400 DA and my worst around 2400 DA.

I did notice something though!!! I had three runs on a test/tune day that were around 150 DA and my times weren't quite as good as my times with the DA around 400. I think everything was pretty equal. Might have been me or the track though, not sure.

When the DA gets that low, the strip needs to be dragged and sprayed several times to get the surface sticky enough. The glue isn't as sticky then, as it will be when it's warmer, when the sun is heating it up.

Also people running street tires instead of DR's or Slicks tear up the prep.

If your fortunate enough to be able to run in good DA, get to the strip early, and try to be at, or near the first few cars to make a pass. If you are at the front, and a pro-mod car is behind you, let him in front of you, you'll have a great groove to run in after his pass.
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