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From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: [FlyRotary] gauges
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
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Date: Tue, 18 Nov 2003 19:10:32 -0500
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>>>A question for Rusty, Todd or anyone else flying a turbo....
I remember Rusty saying he wanted a boost gauge that showed vacuum.  I'm
about to order a boost gauge and I'm unsure what calibration I'm going to
need. Do I need vacuum? Should I be looking for a MP gauge calibrated in
inches of mg, or in PSI. Does it matter?<<<

While I'm not flying a turbo (yet) I'd suggest that you get a standard MP 
gauge with the ability to display as much MP as you plan on boosting up to. 
 We have a Sierra EFIS/EAU combination on the twin-turboed Eagle 540, and it 
displays MP up to about 60" hg.  The Sierra (Chelton) EAU is the same as the 
Grand Rapids Technologies EIS, and you have the option with either one to show 
MAPs up to 33" or 50", the difference being in which version of MAP sensor 
module you get with the install kit.  I personally don't see any reason to 
have boost in PSI in an airplane, as we deal with in-hg for MAP already thanks 
to our altimeters.  All you care about is absolute MAP anyway, just remember 
that 1psi of boost = about 2" hg.  A regular MAP gauge will show vacuum 
already, just pull back the power and watch MAP drop into the teens... that's 
the vacuum that you'd be reading on a vacuum guage.  In a nutshell, the KISS 
principle tells me to stick with MAP using in-hg as that's my mindset in an 
airplane already.  I hope this helps.

     <Marv>