Paul,

    Did you measure the MAP for your p-port Renesis during the dyno
    runs?
      Do you recall the readings you got, particularly at idle
    speeds?  I'm
    questioning the readings I am getting at idle speeds (approx. 2k
    rpm)
    ... around 17".  I measure MAP at the old oil injection
    ports.  The
    three are teed together.

    Mark S.

    Sorry to not get back to you sooner Mark. We had severe email
    problems with earthlink servers.

    I don't recall what those numbers were at 2K RPM. I don't
    think we tested at that RPM. That sounds real high for only
    2000 RPM. What mixture are you  using at that RPM?
    Does the engine idle smoothly at that RPM?

    Is that a steam gage or electronic pressure sensor reading?

    Paul Lamar

    Paul,

    2K is where it starts running rough.  My wideband gauge quit shortly
    after I had to switch to 100LL because of the ethanol mandate.
      So, I'm
    reading mixture off the EM-2.  Mixture is set to where it runs the
    smoothest.  That is about half a bar on the EM-2.  Prior to
    p-porting,
    the engine used to idle down nicely around 1500 rpm.  The engine
    runs
    great at the higher rpms.

    My suspicion is that the primary injectors (and idle) would work
    much
    better if they were located downstream of the slide throttle.  I'm
    currently trying to figure a way to test that theory.

    Mark S.


    I don't expect that will help much.
    I forgot. Are you using a 2.85:1 or 2.17:1 gear box ratio.

    2000 RPM idle is not bad for a p-port. That is 700 prop RPM with
    a 2.85. My O-470 will not idle lower than that.
    Are you having any trouble on approach?

    If so try slipping. Slipping is safer and more accurate way of
    landing
    as one can always extend the glide if you have an engine failure on
    final.

    You should use one of these cheap high speed data aq as it can show
    turbulence in the intake manifold at low RPM. It is sampling at over
    1000 SPS. About the response time of the pressure sensor Tracy
    is using.

    Paul Lamar

    Paul,

    I may be way off on this, but my guess is that at low throttle (near
    idle) settings, and with the injectors being upstream of the slide, much
    of the fuel is puddling in the runner just ahead of the slider.  Every
    so often, a bit of liquid fuel manages to get sucked through causing the
    engine to stumble.  Of course, this doesn't address the MAP readings I'm
    seeing, but it may explain the poor idle.  I would like to try to move
    the primary injectors downstream of the slider.

    I would like to try monitoring the MAP.  Can you provide more info on
    what's needed to do this?

    Thanks,
    Mark


    Historically the way to get a good idle with a p-port engine is use
    two ports. The second, much  smaller port is on top of the big one
    so the timing is later as in this NSU RO80/Spider. I drove one of
    these p-port engine cars in Germany and the idle was very smooth.
    The car pulled away from a dead stop without stumble.

    The port diameter can be as small as 3/4 or 1 in diameter and can
    stay wide open all the time. The main slide throttle would be totally
    closed for idle. The primary injectors can go in the small
    idle air tubes. The manifold pressure tap can stay where it is.

    Guaranteed to work. What would work better in theory than even
    this is a small one way ball valve that would close to prevent
    a small amount of back flow at full power.

    How important is a good idle?


    Paul Lamar




    Paul,

    I think the root of the problem may be a vacuum leak around the hole
    where the throttle cable protrudes through the slide throttle frame.
      Any idea on how to seal this?

    Mark

    Small O-ring? I doubt that as Tracy's EFI does not really care where
    the air comes from. It is setting fuel based on the total air
    getting into the engine. The amount of air coming from there is
    minuscule.
    Have you looked in the intake manifold and seen how much open area
    is in there when the slide is set for idle?

    Try those small holes in the base of the slide first.

    Paul Lamar


Paul,

There is almost no perceivable space in the bores at idle setting.  I
agree with the suggestion of drilling 3 small holes (one per runner) in
the slide.  I had considered doing that to help during idle.

As for the air leak... During idle, the 2" hole in the teflon slide for
rotor #1 moves very close to the hole in the frame for the cable.  This
could provide a path for the air to bleed into the #1 rotor causing it
to run lean.  This may account for the higher than normal MAP as well as
a mismatch in air-fuel mixture during idle.  It would become less of an
issue as the throttle is opened, exactly as I am experiencing.  I
suppose I've got it tuned as well as possible, but with this condition,
I don't see how I will ever get it to run well at low MAP.  It shouldn't
be too difficult to install a small seal.  It sure wouldn't hurt
anything.  I could probably stuff a small piece of shop towel around the
shaft for a down-and-dirty test.  If the idle improves I'll know that
I'm on to something.

Mark S.

A seal would be worth a try in that case.
For future use do you have room to make the slide an inch or so longer?

Paul Lamar