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,

Well, based on the information you provided, I ordered three pressure
sensors and the data logger.  We'll see what's going on once I get the
test setup hooked up.

The more serious issue (other than rough idle) is there is a very
pronounced stumble when going from closed throttle to off-idle, like
when you're attempting to taxi.  Once the rpms come up it runs pretty
good.  Worse case scenario is when you do a landing and roll out and off
the runway, then try to accelerate for taxi.  It is like all the fuel
has pooled on the upstream side of the slide throttle and then when you
crack the throttle open all the fuel pours into the chambers causing the
engine to stumble.  After it has cleared out, it is somewhat less
pronounced.  Is anyone else flying behind a p-port engine?  Are they
having these problems?

BTW, I'm running Tracy's 2.85 psru.

Mark S.

Drill small holes in the bottom of the slide to allow the fuel puddle,
if there is one, to pass. My guess is 1/16th to 1/8th.

BTW if you implement the small 2nd P port measure the area of the current slide opening at idle to get an idea of the small port area you
need to pass enough air keep the engine idling. You want to make the small p-port as small as possible.

The throttle response will be definitely  better if the injectors are
closer to the port. The down side to that is a slightly worse BSFC.

Paul Lamar