Here is my concept of a slide throttle

that I am building for my Kis Cruiser. This for a turbo down stream
from the compressor but I have since decided to make it larger to

mitigate

the air friction losses in the long air pipe to the intercooler.

Paul Lamar

The slide valve throttles on Cosworth engines will hang up if just a

dash of crud gets into the little rollers under the slide. Keep it loose
and sealed from dirt.

I note that many people are leaving much power on the table. The ends

of the runners where they enter the plenum should have the look of a
trumpet bell. The radius should be at least two diameters of the pipe
being supplied. A sharp corner at the inlet will flow about half what a
well radiused tube will flow. Get on a flow bench and try it. If the tube
prodrudes through the wall of the plenum it should have a fully radiused

bell shape as seen on the "Twinn Induction" web site.

A fragment of pop rivet stem, a tiny piece of a stone, a chunk of

featherfill or a safety wire clipping can destroy a rotary before you can
say "what?". I would run an air filter with as much surface area as I
could install. I run a 14" X 5" K&N element. Too big for an airplane but
not too big from the power standpoint. You can't loose power by adding
filter area. If all of the runner ends are radiused the throttle body
will limit engine power and should be very large indeed. If the runners
are not radiused, or poorly radiused then that will limit engine power
and the size of the throttle body doesn't matter at all.

Lynn E. Hanover

Good post Lynn. I totally agree with all of it.

Paul Lamar

  Lets see... the 2 inner runners that enter the plenum wall are 1.25" in
diameter and the 2 outer runners entering the plenum wall are 1.5"
diameter. Add a radiused bellmouth to each of the 4 runners with the
bellmouth radius equal to 2D of the pipe. I come up with a plenum wall that
is 27.5" long. This may be ideal from an airflow standpoint but it sure as
hell doesnt fit my airplane.  :-)

  My intake is most definitely not ideal but I know it will make enough
power to get me flying. Sometime after that I'll probably revisit my
manifold and try to come up with something better. But I doubt it will ever
be large enough to conform to Lynn's ideal and still fit on the airplane.

Mike Wills

You have a tandem seat RV4 and I have a side by side Kis Cruiser. My cowl is wider
than it is high and yours is higher than it is wide :-)
I gots plenty of room over there for a big intercooler/plenum combo.

Paul Lamar
 
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