MAP

[tom cloud]

>
>
>What are sensible MAP values? 
>
Well, lessee: depends on what your sensor reads.  If it reads
absolute, then it would read 0" mercury at pure vacuum and would
read about 29" HG at atmospheric pressure.  Most sensors I know
about read absolute.

If it reads "gauge" (i.e. a reading relative to the current
atmos. pressure), then it would read 0" at atmospheric and
29" under total vacuum.

Your vacuum gauge you have in your tool kit is a bourdon tube
gauge and read "gauge" pressure, not absolute, so, it reads
zero when not connected to anything.  When connected to a
non-blown (i.e. "normally aspirated") engine, it should
read maybe 20" - 24" HG during idle or cruise.  Higher (greater
vacuum) for deceleration, and less for acceleration.

So, one atmosphere = 29" mercury = 760 mm HG = 760 torr = 14.7 psi.
If you're normally aspirated, you only need to measure from about
zero to one atmosphere.  If you're blown -- then ... gotta know boost
pressure.  If 14.7 psi = one atmosphere, then boost of 15 psi means
a total range of 0 to a little more than 2 atmospheres.

Tom