How Much Does Density Altitude Affect ET

[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!

[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

[Jeff Stout]

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]

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]

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]

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.

[Altronics]

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!

[340Cuda]

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!

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

How do you measure the percent of oxygen?

Thanks

[Lenny5160]

Originally Posted by 340Cuda

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

How do you measure the percent of oxygen?

Thanks

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.

[340Cuda]

Originally Posted by Lenny5160

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.

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?