Has anyone used the p port slide throttle with Tracy
       Cook's ECU?
                 After changing my engine to the P port configuration
       with the slide
                 throttle mounted close to the engine the ECU does not
       work.
            There is no
                 good pick up point for the manifold pressure sensor
       hose. The hose
                 connected between the engine and slide throttle gets
       the rapidly
                 fluctuating impulses and also fills with fuel from the
       injectors.
                 Are there any engines running with this ECU and slide
       throttle
            set up ?

                 John Prendergast

                 Mark Supinski is trying as we speak. Any day now. We
       had it running
                 on the dyno
                 but I ran out of dyno money before we got it tuned
       properly. The
                 engine would start easily
                 and run but the mixture was all over the map..pardon
       the pun.

                 Since then Tracy has changed
                 the computer a lot. I suspect the problem may have
       been >>when<<<
                 Tracy was sampling the
                 intake manifold pressure. He only takes one sample per
       rev so it is
                 only a few
                 microseconds long. IMHO many samples should be taken
       and averaged.
                 The same thing
                 might be possible by hooking up the two pressure taps,
       one from
            each
                 rotor,
                 to a vacuum can to smooth out the pulses. Slide
       throttles don't
            give
                 good
                 intake manifold pressure signals when they are wide
       open as
            there is
                 little
                 pressure loss in the intake system. That is why they
       make more
            power.
                 All of Tracy development has been done with a plenum
       on the end of
                 the tubes
                 sampling the pressure just after a single throttle body.

                 If your vacuum lines are filling with fuel something
       is wrong
            with where
                 they are mounted. We did not have that problem. Here is a
            picture of
                 our set up. Can you send some pictures of yours? Where
       are your
                 injectors located?

                 You can also try the apex oil injector ports in the
       rotor housings
                 for a place
                 to sample the intake vacuum... if any :)

                 Paul Lamar ...No rotor no motor.

            The injectors are located in a similar position as in your
       pictures
            except the elbows go forward and then down to clear the
       cowling. The
            vacuum pick ups are  located between the slide throttle and
       engine.
            I believe the  compression wave generated is causing the
       problem. The
            vacuum gage shows such a rapid large fluctuation at the low
       rpm range
            that it would destroy the gage in short order and stops
       fluctuating
            after a short period when the hose fills w/ fuel. The ECU
       T's off the
            same hose which of course could not function properly with
       these
            conditions.

            The Slide throttle plate is so close to the engine that I
       believe the
            pressure wave bounces off the almost closed plate causing
       the rapid
            fluctuations and the pushing of fuel into the hose.
            With the original configuration the throttle body was
       farther away
            allowing a larger volume of air to modulate these vacuum
       and compression
            wave pulses and the injectors were located at the engine
       not before the
            vacuum pick up point as it is now.
            John Prendergast

            ----------------------------------------------------------
            I agree with you on the pressure waves.
            Try smaller hoses feeding into a large can located some
       distance away.
            What you are interested in is the average pressure and not the
            instantaneous
            pressure. I am amazed the gage is responding that fast. Is
       it silicone
            fluid filled?

            What size hoses are you using now?
            We used soft silicone hose which is very flexible. A
       restrictor in
            the hose will
            also work. Drill a small pin sized hole through a piece of
       aluminum
            or plastic rod
            that fits in the hose. You have got to get rid of those pulses
            as no telling what the pressure sensor is reading as it is only
            sampled for a few  millionths of a second.  Only Tracy
       knows when.

            The first length of the hose could or should be larger
            so capillary action of the fuel will not occur.  If the hoses
            are coming out of the top of the intake tubes the fuel
       should drain
            back out no problem.

            Does the hose come off the top of the tubes? We did not
       have trouble
            with
            fuel in the hoses as far as I could tell.

            Mark Su, Please check and see if you are getting fuel in
       your hoses.

            Perhaps we can talk Tracy into a mass airflow sensor
       mounted on the
            input to the plenum. Mass air flow sensors put out a zero to
            five volt signal just like the pressure sensors. However
       they have
            a long time constant as they basically measure temperature
       of a hot
            wire
            and that does not respond to rapid changes in air flow. It
       automatically
            averages out the air flow velocity.

            BTW what does your mixture look up table look like? Perhaps
       you can
            share yours with Mark Su to get him in the ball park
            as your engine is running.



       I have also found fuel in the manifold lines. Not a whole lot, but
       definitely present.  Sounds like I'll have to mount a can of
       some sort
       upstream of the pressure regulator to absorb the pulses.

       John -- One thing I would check first is to confirm exactly what
       fuel
       pressure you are running to the injectors.  I discovered that I
       appear
       to be running 45psi instead of the desired 35psi - so this could be
       causing the flooding problems I am also experiencing.

       Note that I have in fact had the engine running pported with Tracy's
       ECU.  I got it going last summer.  Very tough to get it firing
       the first
       time.  Once I got it to run the first time, I had a much easier
       time of
       it subsequently.  Makes me wonder if fuel in the manifold lines got
       'sucked out' after the first run & combined with clean spark plugs
       allowed easier starts after the first.  I had quite rough
       running below
       2850 engine / 1000 prop.  I am now further wondering if some of that
       roughness was due to the pressure pulses being discussed here.

       I'm stalled on further startup attempts until I get my EC2 and
       EM2 back
       from Tracy - he's updating them to the latest rev so I have all the
       nifty new EC2 diagnostic modes & the auto-programming mode for
       the EM2.

       Mark (Rocky Mtn High)

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   Making the computer take multiple samples might be harder than just
   doing a little analog signal conditioning on the sensor data.
   Multiple samples burns CPU time - maybe not critical, admittedly.
   If the pressure pulses feeding the sensor can be damped such that
   there's no resonant effects in the sensor system (to keep the sensor
   from ringing), doing a little signal conditioning should be easy.

   How are the sensors wired?  Are they a variable resistance like an
   oil pressure?  It might be as simple as adding an appropriately
   sized capacitor to make a low pass filter.  Just need to filter out
   the frequency content that's near the operating RPM of the engine.


   Regards,

   Matt-



I am replying to my reply..  Sorry.

Now that I think about it more, in order for digital sampling systems to
function properly, they must work around Nyquist's Theorem.  That is,
the sampling rate must be 2x the highest frequency content of the signal
being measured.

http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem

What this means is that if Tracy's (or anybody else's) system is
sampling the MP (or any other signal) once per cycle, the samples must
be synchronized with the intake events (probably a tall order given
intake dynamics timing changes with RPM, and as Paul said, intake
configuration).  Or, the computer must sample and average often enough
to guarantee that it sees all frequency/amplitude content of the
pulses.  Or (the easiest option), the frequency content of the analog
signal needs to be filtered such that it's significantly less than the
sample rate..

It's not just a good idea, it's reality.


Matt-

I agree with this Matt but two samples are better than one.
We are really not interested in the shape of the pulse  at this
time. We just want to know what the average manifold pressure roughly is.
As the software is set up now it could be anything. From zero to 29 inches of
mercury depending on exactly where on the wave it was sampled.