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