What Defines Altitude?

[DmaxHawk]

We all know that the barometric pressure is greater the closer one gets to sea level. So how does EFI differentiate between altitudes? Is it through barometric pressure?

We'll I'm up here in the mountains of Alto, NM (Elev. 7396 ft according to NOAA) with nothing to do so I decided to run some numbers. My home is about 120 miles away in Mesilla, NM (Elev. 3877 ft again, according to NOAA). --I'm going to say "according" a lot in this writeup because it makes me feel like a scientist .-- Also according to NOAA, the current Barometric pressure in Alto is 30.44 inHG and in Mesilla it is 30.34 inHG. This translates to 14.95073 PSI for Alto and 14.90161 PSI for Mesilla. Now based on these numbers, EFI would still use LOW altitude tables for both Alto and Mesilla according to B0202 until Baro reaches roughly 13.5. Am I correct?
Thanks

 

[JoshH]

I think your information is incorrect. When I was living in Idaho at an altitude of around 3000' I saw baro pressures in the range of 13.0 to 13.3 psi. Now that I'm back in Texas at an elevation around 500' I see baro pressures right around 14.3 to 14.5 psi.

 

[DmaxHawk]

Am I incorrect or is NOAA?

http://forecast.weather.gov/MapClic...te=EPZ&textField1=32.2702&textField2=-106.807

http://forecast.weather.gov/MapClic...=ABQ&textField1=33.399&textField2=-105.68&e=0

Would humidity have anything to do with it?

 

[JoshH]

Try using EFI to read what your truck says the barometric pressure is. That's what is going to determine what altitude tables you run on.

Here's a table that might help: http://www.sablesys.com/baro-altitude.html

 

[DmaxHawk]

I will. Thanks! Something is not making sense if noaa is reporting almost the same baro...

 

[Trippin]

According to table B0202:
High = 8.5-12.0
Med = 12.0-13.9
Sea = 13.9-15.1

 

[DmaxHawk]

According to table B0202:
High = 8.5-12.0
Med = 12.0-13.9
Sea = 13.9-15.1

Yes I realize that, the thing is that both altitudes are being reported to having almost the same baro pressure ~14.9 psi according to NOAA.

 

[Trippin]

Yes I realize that, the thing is that both altitudes are being reported to having almost the same baro pressure ~14.9 psi according to NOAA.

NOAA is corrected altitude for weather purposes.

Believe in the Baro sensor already on your truck. Check out it's reading with the EFILive Scan tool.

 

[DmaxHawk]

NOAA is corrected altitude for weather purposes.

Believe in the Baro sensor already on your truck. Check out it's reading with the EFILive Scan tool.

Ahhhhhh...I didn't know that! It makes sense now!

Thanks Guy!:hug: 'preciate it!