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

Paul,

I don't have the plenum dims handy.  I will have to wait until next
weekend to measure it.

Mark

Taps on the way.

Paul Lamar



Mark,
The old plenum looks much more aerodynamically correct, the new one
looks to disrupt the intake tube airflow. not straight down the
middle, asymmetric if you will. no numbers to confirm this but the new
unit makes the airflow "do too much".Regardless of whether this is
the cause of your your problem or not it. Remember a good breather
starts at the intake tube and finishes at the exhaust.. My nose has
never worked as good since I bent it!
On a side note Paul, have you read the article on anodizing and
fatigue life on the www.experimentalhelo.com site ,thought it might
interest you it is an interesting read on a crash investigation. Look
at left column for link.

Graeme Riley