Industrial Metals Supply in Burbank CA
Has 4" by 4" by 1/8 wall 6063 T5 aluminum extrusion in stock. Perfect
for plenums. $2.74 a foot and they will cut it for you.

I have a couple of Mazda throttle bodies so I decided to use
one. It is less than optimum aerodynamic wise and heavy but it
will form the base line pressure drop for the dyno engine.

More later on attaching the stock throttle body to the four inch
plenum.
There is a trick to it.

Paul Lamar

Here is the problem and here is the solution. Note how the stock TB
mounting
holes are incompatible with the four inch square plenum extrusion.
Simple solution; weld a 1/2 inch thick plate on the end of the plenum
and drill and tap it for 1/4 inch TB mounting screws.

Paul Lamar

On second thought here is a much, much better solution. Where is it
written
that a butterfly valve must be round? I don't know where I get these
brilliant ideas.
They just occur at random. This is the easiest to build, lightest
and cheapest to build throttle body you will ever see. Major
breakthrough.

I extended the four inch square extruded tube plenum four inches
further
forward and used a square butterfly.  Further more the stock double
hole butterfly
shaft just happens to have a four inch long slot. Perfect for our use.
Major
breakthrough.

It takes about a half hour or less to make this throttle body.
The square  butterfly itself is sheared out of .049 sheet steel. What
could
be simpler to make?

If you want to get fancy you can add a couple of small instrument ball
bearings
to the shaft.

Paul Lamar

OK here it is on the engine. I need to trim some off the motor plate or
move the butterfly back inside the plenum a couple of inches and
shorten it by
two inches which will work fine. Currently it is 16 inches long and
it can be 14 inches. Live and learn :)

BTW the stock TB is four pounds. So far this plenum
and TB is 3 pounds. The nuts will be replaced with nut plates. You don't
want your engine to swallow a nut.

Also BTW this four by four by 1/8 wall extrusion would make a great
coolant pressure tank. Should withstand 30 psi no problem.

Paul Lamar

And if pressure drop across the butterfly is a concern for you, you can
always install another at the other end!  :)

Chris Cosman

Yea but any air blowing in one end can blow out the other end :)

In all seriousness Klause saw my butterfly valve and commented that
a 1/2 inch of manifold pressure was worth 5 MPH on his airplane.
All real fast airplanes have ram air scoops since 1939.
That applies to Tracy's Crook and Saylor as well as Dave Anders.
All flying RV's

Paul Lamar
 
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