Air pressure at diff Alt. - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

kandyflip445 · 05-04-2003, 01:35 PM

Does anyone know how to correct for your air pressure at any altitude other than sea level?

A formula would really help.

Chernobyl · 05-04-2003, 07:17 PM

Best I could find in my physics book is that pressure decreases exponentially as you go up in altitude. At a height of about 5.5km (18,000 ft), the air pressure is half its value at sea level. If we go up another 5.5km to 11km, the pressure is again halved so that it is one- fourth its value at sea level, and so on.

My trusty TI-83 tells me the regression equation (from 5 data points) for pressure due to altitude is:

P=101.3*0.882^h

P is pressure in kPa (kilopascals)
h is height in Km

I'm sure there is a much easier way to calculate these things, but it was pathetically fun deriving this. Hope it helps.

Good rule of thumb I've heard is that cars lose 3% of their total HP for every 1000 feet gain in elevation.

-Alex-

kandyflip445 · 05-04-2003, 10:05 PM

Thanks. I lost my physics book so I had to ask. I'm trying to compare turbos.

Even though I don't have the money yet. I'm surprised no one else posted on this. I thought there were some Physics majors on Zilvia, but I guess that was another board. Thx again.

05-04-2003, 01:35 PM	#1
kandyflip445 Post Whore! Join Date: Sep 2002 Location: Arden, NC Age: 40 Posts: 4,460 Trader Rating: (1) Rides Gallery: kandyflip445 Feedback Score: 1 reviews	Air pressure at diff Alt. Does anyone know how to correct for your air pressure at any altitude other than sea level? A formula would really help. __________________ My 240 vBgarage

05-04-2003, 10:05 PM	#3
kandyflip445 Post Whore! Join Date: Sep 2002 Location: Arden, NC Age: 40 Posts: 4,460 Trader Rating: (1) Rides Gallery: kandyflip445 Feedback Score: 1 reviews	Thanks. I lost my physics book so I had to ask. I'm trying to compare turbos. Even though I don't have the money yet. I'm surprised no one else posted on this. I thought there were some Physics majors on Zilvia, but I guess that was another board. Thx again. __________________ My 240 vBgarage

05-04-2003, 07:17 PM	#2
Chernobyl Zilvia FREAK! Join Date: May 2003 Location: Denver, CO Age: 42 Posts: 1,563 Trader Rating: (6) Feedback Score: 6 reviews	Best I could find in my physics book is that pressure decreases exponentially as you go up in altitude. At a height of about 5.5km (18,000 ft), the air pressure is half its value at sea level. If we go up another 5.5km to 11km, the pressure is again halved so that it is one- fourth its value at sea level, and so on. My trusty TI-83 tells me the regression equation (from 5 data points) for pressure due to altitude is: P=101.3*0.882^h P is pressure in kPa (kilopascals) h is height in Km I'm sure there is a much easier way to calculate these things, but it was pathetically fun deriving this. Hope it helps. Good rule of thumb I've heard is that cars lose 3% of their total HP for every 1000 feet gain in elevation. -Alex-