How Much Does Density Altitude Affect ET
 

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

Re: How Much Does Density Altitude Affect ET
 

Give this a read. Your results may vary.

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

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.

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.

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!

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

Re: How Much Does Density Altitude Affect ET
 

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

Re: How Much Does Density Altitude Affect ET
 

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

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.

Re: How Much Does Density Altitude Affect ET
 

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.

Re: How Much Does Density Altitude Affect ET
 

So at the same DA the percent of oxygen can be different?

How do you measure the percent of oxygen?

Thanks

Re: How Much Does Density Altitude Affect ET
 

There are many different combinations of Temperature, Relative Humidity, and Barometric Pressure that will give you the same Density Altitude, say 2500 feet. The car should perform similarly in any of those combinations that equate to a DA of 2500 feet, but it can vary depending on the exact makeup of those measures.

I'm pretty sure your weather monitor needs to have an oxygen sensor if you want that info.

Re: How Much Does Density Altitude Affect ET
 

You have to have a weather station that measures the percent of oxygen. I know Altronics has them as an option.

I mostly look at the humidity and the barometer to make comparisons. The 327 engine that I am running is much more difficult to dial than the 350 that I have. Must have something to do with the shorter stroke.

Re: How Much Does Density Altitude Affect ET
 

Patrick Hale's book is very helpful and has lots of information on this subject.

http://www.dragracingpro.com/site/90...ooks.html#2859

Re: How Much Does Density Altitude Affect ET
 

the link doesn't work for me ???

Re: How Much Does Density Altitude Affect ET
 

Try this one...

http://www.dragracingpro.com/Books.html

Re: How Much Does Density Altitude Affect ET
 

With a oxygen meter there was a company in the Baltimore area the sold them. I will do some digging and post there name.

Re: How Much Does Density Altitude Affect ET
 

Right there with you Jimbo, I just recently came to the same conclusion!

Re: How Much Does Density Altitude Affect ET
 

thanks;)

Re: How Much Does Density Altitude Affect ET
 

What do you use.
DA OR CF
AND WHY

Re: How Much Does Density Altitude Affect ET
 

Typically 200 in DA equals 1 hundredth to my car but humidity and water grains can play a huge factor. An example would be if say the humidity went up say 15% then it may only take 150 in DA to equal the same .01
Data and lots of it can never be underestimated, I have 5 or 6 log books full of it on this combination so if you come by my trailer and see log books scattered everywhere you know I'm lost on what to dial lol!

Re: How Much Does Density Altitude Affect ET
 

I found simply typing the data from my hand held “weather station” into Crew Chief Pro software predicts my old car pretty much dead nuts, after three passes data at a given track. Mine does not give oxygen data. Appears to me it is not that important. I’m very old, of course, so probably just do not know.

Re: How Much Does Density Altitude Affect ET
 

computech ?

Re: How Much Does Density Altitude Affect ET
 

Racing in these two different conditions: Which one will you be quicker and faster in?

1. 29.00 Baro 900 feet DA
2. 29.80 Baro 900 feet DA

Re: How Much Does Density Altitude Affect ET
 

Is this a TRICK question...?

Re: How Much Does Density Altitude Affect ET
 

No.
;-)

Re: How Much Does Density Altitude Affect ET
 

I didn’t think so ......

Re: How Much Does Density Altitude Affect ET
 

Have not had a chance to look yet but as I remember
Engineered Specialties?

Re: How Much Does Density Altitude Affect ET
 

29.80 will be faster. Barometer trumps everything, except wind.
That’s why sea level tracks are always fast.

QUOTE=HP HUNTER;603829]Racing in these two different conditions: Which one will you be quicker and faster in?

1. 29.00 Baro 900 feet DA
2. 29.80 Baro 900 feet DA[/QUOTE]

Re: How Much Does Density Altitude Affect ET
 

At first I thought there was a conflict in this statement. However are you saying at the same DA the car will perform similarly but not exactly the same depending on the differences in the factors that determine DA?

Re: How Much Does Density Altitude Affect ET
 

I would love to be able to comment more extensively right now, but we are busy at PRI Booth #1537!

Stop by and be happy to answer any questions.

I'll try to post some info next week!

Re: How Much Does Density Altitude Affect ET
 

[/QUOTE]

Pretty much what I have seen. Baro trumps the others.

Re: How Much Does Density Altitude Affect ET
 

Yes, it sounds like you understand what I was saying.