Ed Anderson wrote:
Ok folks,
Fired up the engine with the new intake with the polyurethane resin
casting plenum/throttle body -
SNIP
One of my objectives was to reduce weight
and I have shaved off 12 lbs off the old intake with the new one weight
11
lbs with manifold casting, tubes, plenum, throttle body, fuel injectors
and
fuel rail. . Another objective was to clean up the exhaust side of the
block for later putting a turbocharger there. As the second photo
shows,
plenty of room for the turbo now, note how snuggly Paul's casting bolts
up..
Note the oil on bottom of flange from cutting and refitting oil pressure
sensor line.
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
BTW folks I want to clarify something here just so no erroneous
conclusions
are drawn. Strictly speaking Ed is using a dynamic chamber and not a
simple plenum.
I am sure Ed did not intend to mislead people.
Paul is correct, just called it a "Plenum" for lack of a better term.
Here are some pictures Ed sent earlier. I want to go on record as not
recommending
this design. Dynamic chambers with this length of intake runners are
designed to enhance the torque at 2500 to 3000 RPM. High torque at that
RPM is
not needed in an aircraft engine. IMHO this design hurts the ability of
the engine
to generate power in the 5000 to 7000 RPM range.
I agree with Paul on this point - that to get the dynamic charging effect in
the 5000-7000 range the runner length would need to be considerably shorter.
Working on that version as we speak. By the time I understood (with Paul's
assistance, I might add) the dynamic chamber effect and worked out the
calculations for it, my "plenum" design was already locked in and precluded
using shorter tubes due to interference of "plenum" with the block.. So
decided to continue for weight reduction objective and design another
"dynamic chamber" that could be used with shorter runners. One of the
reasons that I chose to use a flange and bolt the tubes to Paul's manifold
rather than weld them - they can be easily changed.
My recommendation is to use a simple plenum or helmholzt resonator
chamber of twice or more of the engine displacement. For the 13B that
would
be 160 cubic inches or 4 X 4 X 10 inches or 3 X 3 X 17 or 3.5 X 3.5 X 13
inches
with a throttle body with a straight shot in from one end.
In Ed's design the air is forced to make a two sharp 90 degree
turns instead of only one.
Not quite certain which two sharp 90 deg turns you are referring to here,
Paul. I presume one is the turn from the throttle body into the tubes. As
there are about 4-5 90 deg changes in airflow from throttle body to port,
not certain the other "sharp" turn, you refer to.
Ed Anderson
Paul Lamar
Basically the airflow wants to come in straight from the front of the airplane.
One of the 90 degree bends is because of that. The other is from the throttle
body to the runner which not much can be done about.
If you align the throttle body in aircraft longitudinal axis and provide a properly
designed scoop you can fully benefit from the dynamic pressure at 200 MPH.
Ideally speaking dynamic pressure at 200 MPH is 104 pounds per square
foot or about .722 psi. 29 inches of mercury is about 15 psi or about 2.4
percent more power. Perhaps as much as 5 hp. No air filter as there would
be a pressure drop across that. Knowing the air consumption of the engine
at 200 HP or so you can size the scoop for minimum loss at say top
speed. A small point perhaps but every little bit helps.
Paul Lamar
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