Miata Mailing List: June 1996, Message #302
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   From: LANCE K SCHALL <76760.2754@CompuServe.COM>
Subject: Re:  Ummm!  Leftovers!
   Date: Tue, 4 Jun 1996 23:17:16 -0400

Bill's sample size of one empirical data point is better than what ever I might
come up with.

But, I can never resist a technical question.  Besides, I now live at 5400 ft in
Boulder having come down to these flat lands from 7000 ft in Flagstaff.

I do not know what formula the web site is using, but keep in mind that as
altitude goes up, barometric pressure AND air density both decrease.  At
different rates!  Further complication can result if we toss in expected
temperature decrease at altitude.  Moisture content of the air is also important
and rarely compensated for in run-of-the-mill calculations.

All that aside an optimistic approximation can be made using just the pressure
ratio:

altitude		pressure
0		14.7
1000		14.2
2000		13.7
3000		13.2
4000		12.7
5000		12.2
6000		11.8
7000		11.3
8000		10.9
9000		10.5
10000		10.1

This gives 12.2/14.7*136=113 for 5000 ft.

In actual real life driving, you do not notice the power loss as much as you
might think.

Lance Schall
Boulder, Colorado
1990 Crystal, MCA # 159