On a normally aspirated engine, the MAP will be about 1 inch
per thousand feet from 29.92 plus about 1.5 inches for
induction losses on a running engine. So if the maximum
observed MAP is 23 inches, you are at about 5,500 feet
pressure altitude [give or take a thousand feet.
Turbocharged engines make such a check impractical.



"Jose" wrote in message
news | No one has mentioned using the manifold pressure guage
as an altimeter.
| Because you can't do it in the air, unless you stop the
engine first.
|
| Well, you can, sort of, but it probably won't help much.
At full
| throttle, the manifold pressure will max out at a value
that has the
| same relationship to altitude as an altimeter. I vaguely
recall it's
| something like an inch loss per thousand feet high.
|
| Jose
| --
| "Never trust anything that can think for itself, if you
can't see where
| it keeps its brain." (chapter 10 of book 3 - Harry
Potter).
| for Email, make the obvious change in the address.