Re: New member, stuff

[rdh@sli.com (Robert D. Houk)]

   All this talk of 2.0bar boost.  Don't the Audi gauges, is there one in the
   dash?, read, I don't know how to word this but in a different value than say the
   stock and HKS gauge in my Xr?  So the 2.0bar you see is about 16-16lbs of boost?
   If you are getting 2.0bar the way my gauges read you better get a helmet! 2.0bar
   for me would be 30lbs of boost. Fast yes, but just once. I run 16-18lbs in my Xr
   or 1.2bar or so.  all that boost without any kind of reworking of the ignition
   timing curve seems a bit risky.  You can't do that in an Xr and we have knock
   sensors.  Talk about spoiling the fun.  

Well, assuming I've managed to parse the language here...

You need to distinguish between "boost" and "manifold pressure" and "ab-
solute" pressure.

Atmospheric pressure == "1 Atmosphere" == "1.0 Bar" == "14.7 PSI" ==
"760 mmHg" == "30 inHg" (sealevel, 70F, more or less; it's been a
*long* time since I studied/knew all these constants by heart).

"Boost" is generally additional pressure above current atmosperic pres-
sure, thus 1 Bar of boost is 2 Bar absolute pressure assuming you start
at sealevel at 70F. If, on the other hand you start at the top of Pike's
peak, you're in a good partial vacuum (anyone know the atmospheric pres-
sure atop Pike's Peak?) of -- I'm guessing -- .7 Bar, so 1 Bar of boost
yields an absolute pressure of 1.7 Bar.

"Vacuum" is generally relative to 1 Atmosphere - thus "10 inches" of
vacuum (as in "inches of mercury") is 20 inHg absolute, or .66 Bar.

"Manifold pressure" can be in any of the above units, and absolute or
relative; kinda like "dB" (deciBels) -- you need to know what the frame
of reference is (absolute power delivered to speakers; absolute level
of magnetism on a magnetic media; 1mw@600Ohms; etc.)

You can safely assume any streetable [legally] passenger car whose gauge
reads 2.0 Bar is absolute pressure [turn the engine off and it will set-
tle at 1.0 Bar or atmospheric, again assuming sealevel and 70F].

Audi gauges are typically (that I have seen, anyways) absolute manifold
pressure, so 1.0Bar is middle of gauge, full vacuum (impossible to ac-
tually achieve in normal car engine) is 0.0 Bar, and 14.7PSI of boost is
2.0 Bar (sealevel, 70f).

					-RDH