A vacuum guage connected to the intake manifold of an engine is a very good way
of measuring the relative power output of the engine. At idle the pressure will
be very negative (high vacuum) and as you open the throttle the vacuum will rise
towards atmospheric, but will never quite get there, unless you boost the engine
with a turbo or supercharger, then it could go above atmospheric.
Now if you really want to have some fun, you could read the vacuum at the
venturi of the carb, in which case the vacuum will be very low at idle and very
high at full throttle, but I don't know what this would tell you!!!!
Also called MAP (manifold absolute pressure) guage in aircraft....very usefull
on a plane engine because the density of the induction air changes so
dramatically with altitude....and of course boost if you are lucky enough to
have it.
How really usefull in Spridget? I dunno.....unless it's boosted then you
really, really want to have one!! Overboosing leads to detonation...detonation
leads to destruction in rather fast order. Anyone out there ever seen a piston
that has severe detonation damage?
Geoff Branch
'74 Meejit "Yellow Peril"
'72 Innocenti 1300 Mini
----- Original Message -----
From <LottMJ1967 at aol.com>
To: <spridgets@autox.team.net>
Sent: Monday, February 23, 2004 3:35 PM
Subject: Vacuum Gauge - Why?
> Listers,
> Have a set of additional gauges that came with my car. One is a vacuum gauge.
My non-knowing question is why would you need this? I obviously understand why
you need oil pressure, water temp., even the ammeter that is included in this
additional gauge set. However this vacuum gauge escapes me.
>
> Thanks,
> Michael Lott
> (usually lurking and learning)
> Compton, CA
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