Paul,

I'm not sure the plenum is the problem as there is a serious MAP
mismatch even at idle.  If it was a plenum flow problem, shouldn't it
be minimal at idle and worsen as RPM increases?  I could verify this
theory by test running it without the plenum.

I still suspect I'm getting some serious leakage somewhere in the
intake, most likely through the slide throttle.  I plan on testing it
with a shop vac and a Uni-syn.  I'll hook the shop vac to one runner
outlet and then check for leakage on the other two; then repeat for
each of the three runners.  Then I will check the flow through each at
idle setting to see how well they match, or not.

Mark


From what I can see from this picture it looks like the plenum.

The engine appears to need a lot of air even at idle.

Get up on something high and take a picture looking down on the
current
plenum. What are the dimension of the plenum?

There is a huge difference in the amount of air the back rotor is
getting
compared to the other 2. We are talking 20% here. I don't think it is
leakage through the slide throttle. The rear rotor is doing a lot
of extra
work. No telling what will improve when this is fixed. The BSFC
could get
significantly better as well as the power. The rear rotor is
running leaner
as Tracy averages the air getting in the engine. The front rotor
is running
richer. If you have EGT's let us know what they are saying.

The non symmetry of the plenum could be affecting the tuning of
each intake
pipe. A higher data sample rate will give us better info on that.

Just take the plenum off and run it with the data acq still connected.

Here is what Mark Suspinski plenum looked like and we were getting
equal
pressure in both rotors.

Paul Lamar


The required volume of the plenum is related to how large the pulses
of air are..  The RPM relationship with plenum volume comes from the
resonant tuning - where the 120% Volumetric Efficiency happens, the
plenum volume will need to be higher.  At high RPM, the pulses just
come more often, which should dictate the size of the inlet of the
plenum.

Here's an interesting discussion - I don't agree with all of the points:

http://speedtalk.com/forum/__viewtopic.php?t=1142
<http://speedtalk.com/forum/viewtopic.php?t=1142>

One person says the plenum should be 1.5x the port volume (all the way
to the rotor face)..  That seems a bit low.


Regards,

Matt-



Paul, I don't understand how the plenum could cause this.  The flow is
something like  20% of WOT flow rate and far below the tuned resonance
frequency.  It seems more likely to me that the there is a difference in the open area of the throttle plate from one rotor to the other.

For instance if  using feeler gauges there is  a .004 gap  on the side of rotors two and three and .009 on rotor one there will be  a lot more
flow on rotor one.  If there turns out to be a difference a rotary air
file should be able to  make them the same.


  There may also be a difference in exhaust scavenging if the
header pipes have different lengths. There has not been much discussion
on exhaust tuning for aircraft installations. A length optimized for
minimum fuel consumption would be a plus  but any length as long as they are the same would benefit idle quality.
George grimes



According to Mark the slide throttle was machined so I could not imagine it was that far off. One can check that easy by just sticking a bore gauge in there. One can also do it by inspection with the throttle wide open and see if all the holes match up.

The pressure differences match up with the plenum geometry.
The input duct to the plenum is opposite rotor 3 that is getting
the most air. The rotor that is getting the least air is the one down the plenum the farthest from the input duct. It is also the sharpest 90 degree turn.

Getting air to turn corners is always a problem.
That is one reason the p-port is worth 25% more power as it is a straight shot into the rotor housing. Especially when the pressure differences are so low as they are in normally aspirated engines. The side exhaust is less affected due to relatively  higher pressure differences.

Air molecules are  like a stream of tiny, sticky, rubber marbles. It has mass, inertia, compressibility  and it adheres to other air molecules like itself. So called "flying" insects swim in air and don't really fly :) That is where the Reynolds number comes into play.

http://en.wikipedia.org/wiki/Reynolds_number

Paul Lamar