Paul,

   I have run this by Tracy and I wandered what you thought of this. This
   is a 4 port 13b in a Cozy III. I was intending to take the intake duct
   to a NACA scoop on the lower left cowling ram air style. The controller
   is a RWS EC2. The actual ducting will be rigid fiberglass with inline
   filter. I am looking for 160 to 180 HP. Good idea? Bad Idea? Start over
   with a dynamic chamber and long runners?

   I would greatly appreciate your comments.

   Steve Denny

   Windsor, Colorado


   BTW Sorry, apparently I can only send one pic at a time so here come
   2 e-mails

   ------------------------------------------------------

   That is the way to do it if you don't have graphic scaling programs.
   Anything over about two meg is too big to send.

   Any Y in the pipes causes a discontinuity. In effect what you wind
   up with is several short pipes resonating in series. This, in
   theory, narrows the torque peak but moves it way up in the RPM band. Perhaps higher
   than 11,000 RPM. That of course does nothing for you. This is an over
   simplification of course so unless you dyno this engine no telling what
   is going to happen.

   I WILL say you will not get as much HP at 7500 RPM or 6500 RPM as
   you would  get if you had just four long pipes of the right length, a plenum
   and this throttle  body.

   You want the torque peaks in the 5500 to 6500 range. That yields the
   best cruise  BSFC and the best power in the 6500 to 7500 RPM range for aircraft
   use. You get that with the pipe lengths in the 25 to 28 inch long range. These
   numbers are also somewhat dependent on the inside diameter of the pipes. A
   smaller dia. pipe moves the torque peak down. Larger pipe dia. moves it up.

   Matt put it very succinctly awhile back but I lost the message.
   Do you remember that Matt? Can you upload it again?

   BTW NACA ducts are not recommended by NACA engineers for carb air.
   You need a true ram air scoop.

   Paul Lamar ...No rotor no motor.



Steve,
I can't see into the TB throat very well, but it appears there is a step
just past the butterfly.  If that's the case I would try to get that
smoothed out as much as possible to promote good airflow.  Just an
observation.

Mark St.



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