How Much Does Density Altitude Affect ET

davidhuff · 12-12-2019, 04:23 PM

I know very little about Density Altitude and was searching for information.

Dustin Ward · 12-12-2019, 05:21 PM

Give this a read. Your results may vary.

https://www.biondoracing.com/tips.shtml

Dave Noll · 12-12-2019, 05:45 PM

My understanding that 1 and 2 barrels swing wider than 4 barrels and low compression wider than high compression and a stock converter (sportsman bracket) wider than a high flash converter, etc, etc, etc, etc . The really good cars may change very little with the weather.

jmcarter · 12-12-2019, 06:19 PM

While I’ve always referenced Biondo’s tips as a guide I would just point out that meticulously keeping notes on all your runs is invaluable to setting up a reliable correlation curve between DA and ET since the host of other variables (i.e. wind) can play such a huge role. I’m just now trying to explore some of the analytics of this and discover that my last year’s record keeping was painfully inadequate. You can probably guess one of my New Year’s resolutions.

Ralph A Powell · 12-12-2019, 08:24 PM

Percent of oxygen changes can have a big impact and since very few measure this the basic numbers can remain the same but the percentage of oxygen can change and have a large impact!

Keith 944 · 12-12-2019, 08:32 PM

On my two cars basically 200 feet of altitude change equals one hundred .01 I run them a little fat so that it will be this way

Jeff Stout · 12-12-2019, 10:17 PM

Quote:

Originally Posted by Keith 944

On my two cars basically 200 feet of altitude change equals one hundred .01 I run them a little fat so that it will be this way

That's pretty good. Im 145ft of change and. 1 ET difference. I run mine just right in the heat then when air gets good car goes lean. That gets me the 145ft average

cmracing · 12-13-2019, 12:29 AM

Quote:

Originally Posted by Keith 944

On my two cars basically 200 feet of altitude change equals one hundred .01 I run them a little fat so that it will be this way

My faster car is about .01 per 300ft running on race gas.

Richard Grant · 12-13-2019, 10:19 AM

My experience has been that if you run around the ideal air/fuel ratio you will see 150 ft equals .01. Or you can run lean and move higher into the 200ft area. It gets hairy as you get leaner and can do engine damage. The only time that I've seen the 300ft range is with ethanol in our bracket car. A normal ethanol car will equal the 300ft per .01 area. If you don't see these numbers or if your car isn't consistent , you probably have a problem that needs correcting.

Dave Muller · 12-13-2019, 11:21 AM

Quote:

Originally Posted by Ralph A Powell

Percent of oxygen changes can have a big impact and since very few measure this the basic numbers can remain the same but the percentage of oxygen can change and have a large impact!

I've been strongly suspecting for a while that this is the case. When I stay near home I can get a pretty good idea from DA and wind but then I go to a different area, where they have those weird tall things (I think they call them trees) and suddenly I'm way off in my dial-in.

12-12-2019, 04:23 PM	#1
davidhuff Senior Member Join Date: Jul 2009 Posts: 928 Likes: 1 Liked 120 Times in 42 Posts	How Much Does Density Altitude Affect ET I know very little about Density Altitude and was searching for information.

12-12-2019, 05:21 PM	#2
Dustin Ward Junior Member Join Date: Feb 2009 Location: Renton Washington Posts: 35 Likes: 27 Liked 4 Times in 2 Posts	Re: How Much Does Density Altitude Affect ET Give this a read. Your results may vary. https://www.biondoracing.com/tips.shtml

12-12-2019, 05:45 PM	#3
Dave Noll Senior Member Join Date: Nov 2007 Location: Div. 6, Eastern, WA Posts: 709 Likes: 2,653 Liked 238 Times in 111 Posts	Re: How Much Does Density Altitude Affect ET My understanding that 1 and 2 barrels swing wider than 4 barrels and low compression wider than high compression and a stock converter (sportsman bracket) wider than a high flash converter, etc, etc, etc, etc . The really good cars may change very little with the weather. __________________ Dave Noll, EF/S ,?/SA 6526 Last edited by Dave Noll; 12-12-2019 at 05:47 PM.

12-12-2019, 06:19 PM	#4
jmcarter VIP Member Join Date: Dec 2008 Location: Richmond Hill GA (and Port Ludlow WA) Posts: 4,287 Likes: 2,350 Liked 3,154 Times in 965 Posts	Re: How Much Does Density Altitude Affect ET While I’ve always referenced Biondo’s tips as a guide I would just point out that meticulously keeping notes on all your runs is invaluable to setting up a reliable correlation curve between DA and ET since the host of other variables (i.e. wind) can play such a huge role. I’m just now trying to explore some of the analytics of this and discover that my last year’s record keeping was painfully inadequate. You can probably guess one of my New Year’s resolutions. __________________ Jim Carter 2340 Super Stock 2340 SST/2340 Stock Set another place at the table

12-12-2019, 08:24 PM	#5
Ralph A Powell Member Join Date: Oct 2017 Location: Bay City Texas Posts: 387 Likes: 2 Liked 225 Times in 136 Posts	Re: How Much Does Density Altitude Affect ET Percent of oxygen changes can have a big impact and since very few measure this the basic numbers can remain the same but the percentage of oxygen can change and have a large impact!

12-12-2019, 08:32 PM	#6
Keith 944 VIP Member Join Date: Feb 2006 Location: Dela-where? Posts: 2,192 Likes: 1,160 Liked 1,874 Times in 576 Posts	Re: How Much Does Density Altitude Affect ET On my two cars basically 200 feet of altitude change equals one hundred .01 I run them a little fat so that it will be this way __________________ KEITH MAYERS 2-1/2 X somebody Still many X nobody

12-13-2019, 10:19 AM	#9
Richard Grant Member Join Date: Jan 2002 Location: West Monroe, La. Posts: 301 Likes: 9 Liked 13 Times in 7 Posts	Re: How Much Does Density Altitude Affect ET My experience has been that if you run around the ideal air/fuel ratio you will see 150 ft equals .01. Or you can run lean and move higher into the 200ft area. It gets hairy as you get leaner and can do engine damage. The only time that I've seen the 300ft range is with ethanol in our bracket car. A normal ethanol car will equal the 300ft per .01 area. If you don't see these numbers or if your car isn't consistent , you probably have a problem that needs correcting. __________________ Richard Grant 4988 STK