> 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.
     >
     > I DO NOT disagree with you on merely changing the map table entry to
     > correct for this effect. It would be better however if we did not
    have
     > to do that 128 times. One for each .12 psi increment in the intake
     > manifold pressure.  It would be better if the computer would
     > set the mixture on the basis of the actual mass of air entering
     > the engine at any RPM. That is exactly what a mass air flow
    sensor does
     > in an automotive EFI system or a carburetor does for that matter.
     >
     > I think Tracy could do it by taking five or ten equally spaced
    pressure
     > samples during the time the port is actually open and integrating
    them.
     > Then add or subtract that number from the atmospheric pressure in the
     > intake manifold. The  computer is fast enough to do this no
    problem. It
     > can probably get a sample in a few millionths of a second since
    it runs
     > at 33 million instructions per second more or less. I am sure it
    is now
     > twiddly its thumbs most of the time.
     >
     > To Tracy credit there is an auto tuning mode where the
     > computer looks at the O2 mixture monitor installed in the exhaust
     > pipe and adjust the MAP table entries accordingly. I have not
    tried that
     > yet. That might solve the problem. I can see a scenario when
     > descending where that might not work. If it were me I would
     > also look at the EGT to get a better feel for what the
     > engine was doing.
     >
     > Paul Lamar
     >
     > Wish I had time to discuss this at length  but alas, I don't.
    Working
     > on other stuff like stand-alone auto-tune, knock sensor handling and
     > have to actually build this stuff : )
     >
     > The EC2 was designed with a plenum manifold design but FWIW, it would
     > work in this scenario just fine if the sample were taken at the peak
     > pressure point.  Just need to know exactly what time it occurs.
    Will be
     > interested in the results of your tests if it happens.   Knowing the
     > absolute value of peak would help to set the initial flow rate in
    Mode 3
     > but not a 'must have' item.
     > Tracy (replacing a failed LS1 coil on my plane today)
     >
     >
     > --------------------------------------------------------------
     >
     > Thanks for your input on this Tracy. The problem with two P-port
     > pressure taps "Teed" together like we are using now is the runner
     > pressure pulse data is 180 out of phase from runner one to runner two
     > thereby canceling some of the pressure.
     >
     > I was just thinking about using two pressure sensors one on each
     > runner and an auxiliary  PIC to process the info and send you
    corrected
     > pressure data when you need it.
     >
     > So far I have not figured out how to do the second part.
     >
     > ..... Wait a minute.... I just got it!!! Use the first
     > RX7 gen vac solenoid valves to switch the hoses in time with the RPM.
     > That might work. I could condition and amplify your ignition
     > pulse to switch hose connections. Forget the aux PIC.
     > I'll have to check the speed of those valves. I have plenty
     > lying around.
     >
     > The ultimate p-port solution is two separate pressure sensors.
    One for
     > runner one and one for runner two. Mount the sensors on
     > the manifold and run wires instead of hose for quicker response.
     >
     > Paul Lamar



    Except as a diagnostic tool, is it critical to get separate MAP data for
    each rotor?  Why not take the peak reading from one of them and
    assume the
    other one is going to have the same value?

    I am starting to get it.  I had an epiphany (well, maybe not, but..
    ) last
    night as I was going to sleep, and Tracy's comment confirmed it.  I was
    considering the case of having the throttle on the cold side of the
    plenum.  In the case of having the throttle close to the port the
    measurement of MAP is different.  There is very little volume in the
    system between the throttle and the combustion chamber.


    Regards,

    Matt-

    Sampling only one might work. We need to try that. We can watch
    the EGT'S and see if they are nearly the same.

    Problem is Tracy samples (for this rotor's injector pulse width)
    right about the time  the exhaust port opens. (20 degrees before TDC
    on the other rotor.)  Not optimum when the pipe is on song. (Is
    resonant)

    I need to talk him into moving the sample in software. That
    should be easy and not affect the plenum systems.

    Paul Lamar

    That's more or less what I had in mind.  It's easy to change & use
    one sample for both rotors and would not cause any problems in
    aircraft applications.

    Bill Dube' sent me the Renesis injector flow rates and I was a
    little surprised to see that the yellows were rated less than the
    Blues.  4 Blue injectors would work fine but 4 yellows are running
    close to the limit at 8000 rpm.  Above that, I'd use the 6 injector
    solution I outlined before.

    Tracy