> Not exactly. Think of things in absolute pressure terms. We are
     walking
      > around in 15 psi pressure at sea level. That is 30 inches of

mercury

      > using a manifold pressure gage. Our body would be crushed if it
     were not
      > for the same pressure being in our lungs.
      >
      > Now what happens in the intake manifold due to an organ pipe

tuning

      > effect is the PEAK pressure pulse may go up to 200% of
      > 15 psi or 30 psi (60 inches of Hg). 100% more than wide open
     throttle.
      > When the port is closed at the RPM tuning point the pressure also
     goes
      > below 15 psi (30 inches of Hg) for awhile. Perhaps all the way to
     zero
      > pressure.  The average is still 15 psi  (30 inches of Hg).
     Remember the
      > throttle is still wide open. The key word is "PEAK". What we are
      > interested in is the amount or mass of air that flows into the
     engine.
      > That is proportional to the area under the peak plus the
      > the air flowing into the engine due to atmospheric pressure alone.
      >
      > If the shape of the pulse were a right triangle the area would
      > be 1/2 base times height or 7.5 psi so to speak. That would
      > be 50 percent more air or the equivalent to 22.5 psi (45 inches
     of Hg).
      > In the real world we don't really see that much air. What we see

is

      > about 20% more or the equivalent to 18 psi (36 inches of of Hg).
      >
      > Using the term vacuum confuses the issue. A pure vacuum is just

the

      > absence of pressure and what one would get in outer space.
      >
      > BTW pressure at sea level expressed in psi is  merely the weight

of a

      > long, one by one inch,  column of air up to the start of space
      > expressed in pounds. In other words the column weighs 15 pounds.
      >
      > I don't mean to be condescending here I just don't know the level

of

      > Physics education of every one on here. I am trying to explain

things

      > from the most basic level possible.

Big cut VJ
We were faced with a similar problem in experimentally measuring the total
impulse
of very short thrust pulses of attitude control rockets. We ended up using an
integrating voltmeter "gated" to the time of interest. Virtually all digital
voltmeters
generate a frequency based on voltage and counts that over a time (I think)
"Gating" such a circuit over the port open time would give a pretty good
measure of total charge - and that is what you want to base the injected
fuel on.
Just my nickel - butting in
Vance

---------------------------------------

No I appreciate the advice Vance. No substituted for your extensive
experience in these matters. I will give it some serious thought.

Let's see if I understand this. These voltmeters generate an increasing
signal frequency as a function of the voltage they measure. Is that a correct
statement? Basically it sounds like a voltage to frequency converter. Gate
the frequency generator on during the time the port is open and read the total
count. I did something similar when I was measuring speed with
my computerized automotive road test system. No software math of
any kind required.

Sounds great. The question is how do we get the number into
Tracy's existing computer. Tracy's computer is currently designed
to take an analog voltage from .5 to 4.5 volts as a measure of
the intake manifold pressure.

I will have to think about this some more.

Paul Lamar