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

It is possible the V notches you put in the slide are not exactly the
same size.  A small size difference could be a major flow difference
at idle.  Try the Uni-syn to see what difference there is in the flow
or draw.  At this point the only way to balance the flows is to file
a small bit off the low flow and try again.  The vacuum will work to
test flow, off the engine.  I know a fellow who flowed heads that
way.  A water manometer will also work well.


Dale Davies