Ed,
Great news. When I first postulated variable length intakes,
I never dreamed the idea would get this far, certainly not this fast.
Someone with a turbo might be able to tell us how much equivalent boost
400-500 rpm represents - 3 or 4 inches?
<... had I been able to extend it
to 50" I would have been able to pick up another 100-150 engine rpm ...>
Sounds like you are implying that
you have arrived in the lower end of the EDDIE "power band" and that with
a little airspeed the rpm would increase another 100-150 rpm. Am
I reading you right? Given what you know now about charge temp (you
estimated ambient + 55F I believe) What would you calculate to be
the runner lengths (or more important, delta L) for ambient temps of 0F
and 90F? I would intuit that these are pretty much the envelope in
which we would be operating.
<... when the pulse starts
to round the curve this causes additional pressure on the walls of the
path ... pushed by the outside of the path wall to change the pulse
direction ... my air inlet from the throttle body is in that same region
.... some of the pulses energy is blasting out the throttle body port ...>
I couldn't see that well in the picture,
but would it be possible to have your TB hanging down the inside
of the "U" between the runners? If the "centrifugal force" on the
mass of the charge is indeed making it "bunch up" on the outside of the
turn, it would seem the inside of the turn would be a more ideal place
for the TB to reside. A lot to ask, I know, what with all the extension
mechanism there and tight space to begin with.
What you've got here is a triumph
by any measure!! ... Jim S.
Ed Anderson wrote:
Hi
Folks,
Well, I have now conducted 12 ground runs with my new variable length intake
manifold. This was a prototype using some old manifold components
I had laying around for the lower manifold (see photo of slab lower
manifold). The maximum port to port length of the manifold was restricted
to 47.8" as a results of using some of these make-shift components.
My design calls for one able to extend this distance to 51-52" which I
could not do due to limited space and these components. The turn
from the my lower manifold into the block is not optimum as it makes a
90 deg turn with no inside radius - certainly not conducive to good airflow
there.Also my throttle body plenum has less that an optimum air path from
throttle body to the runners. Now
with the caveats out of the way here is the bottom line. My
91 street ported turbo II has Tracy's 2.17 gearbox and swings a 68x72 Performance
Prop - this is the same set up that Tracy Crook has on his Rv-4.
My nominal static engine rpm is (not too surprising) is the same as Tracy
has reported 5200 rpm. So that is what I take as my baseline. With
the variable length manifold at its full extension of 47.8" inches (port
to port) the distance from intake port to throttle body is 1/2 that or
23.9" for those who might be wondering how I stuffed 47" under the cowl. At
that setting and with the OAT at 65F my static rpm increased from 5200
to 5600 rpm or a 400 rpm increase. That of course equates to approx.
200 rpm increase in static prop speed. I believe that had I been
able to extend it to 50" I would have been able to pick up another 100-150
engine rpm. My fuel flow while the engine howled at 5600 rpm (really
had the RV bouncing and a rocking) was between 16.5 - 17 GPH. My
best estimate based on the numbers is that the engine picked up 12-17HP.
When I decreased the length of the intake from its 23.9" to 21.4"
the rpm dropped back to 5200 rpm indicating (as I would have expected)
that the shorter length raised the EDDIE RPM out of the reach of my static
rpm range. My equations
indicated that assuming a 55F increase in air temp from OAT (65F) to a
manifold temp of 130F (I had previously used 180F for the calculations
but am now convinced that's a bit on the high side for the air temp inside
the intake manifold) that for the full extension of 23.9" length,
that the EDDIE RPM would occur at an rpm of 5650. This appears to
correlate well with the 5600 rpm I observed. The minimum length
of 21.4" would have an EDDIE rpm of 6500. 6500
rpm is of course much higher RPM than I can reach on the ground (with a
prop {:>)). It appears that the 5650 EDDIE rpm was close enough to
pull my static rpm up into that "EDDIE bucket". However,
it was not all peaches. I had hoped that my aluminum tubes sliding
inside aluminum tubes might not require Nickel plating as I originally
planned. In the work shop the tubes slide inside each other without
any problem. On the aircraft, however, after 12 ground runs, I noticed
that the tubes were beginning to fret in places. It appears
that the pounding on these tubes caused by the DIE pulse as it races from
intake to intake is considerable, either that or perhaps the vibration
combined with the sliding action is the cause. In any case there
is fretting, the end results is that the tubes began to show signs of unequal
drag as my small 1/90 HP motor started groaning. The rectangular
tube that houses the movement mechanism also needs to be mounted more rigid.
So while I would have liked to have make a couple of flights to evaluate
the higher rpm operation before going on to the next design, it was not
to be. So although
disappointed I was unable to test the EDDIE at higher rpm, I am satisfied
with the results of the prototype and plan to go to the next stage of building
with a new lower manifold with better airflow and to lower it a bit so
I can get the extra couple of inches in. My
initial thoughts for the next manifold is to use one of the aftermarket
IDA Webber type manifolds that I believe Paul Conner and Rusty used.
This would replace my "slab" lower manifold providing improved airflow
in that region. I believe it would also lower the profile of the
intake permitting me to add another couple of inches to the runners.
The Webber manifold I am currently using has the centers of the tubes 90mm
apart. At the top of the tubes where the throttle body is attached
is the path is also 90 mm (approx. 3.5") apart which I believe does
two undesirable things. There is insufficient room for a good airflow
route from the throttle body to each individual tube and the manifold path
is curved a tight 180 deg to round the top and connect the two parallel
tubes. My suspicion is that when the pulse starts to round the curve
this causes additional pressure on the walls of the path in that
area as the outside of the pulse is now being pushed by the outside of
the path wall to change the pulse direction rounding the curve and going
to the parallel tube for the other port. Since my air inlet from
the throttle body is in that same region, I suspect that some of the pulses
energy is blasting out the throttle body port. I believe that may
be one reason why Mazda has their manifold "round the curve" before the
throttle body opening. The
IDA Webber aftermarket manifold has a 120mm (4.7") distance between its
openings which would provide more room for a better airflow path from the
throttle body and a less drastic 180 deg curve for the pulse. So
the bottom line is I was not able to fully test the prototype as I had
hoped and I clearly will need to have the tubes nickel plated to hopefully
prevent the fretting and galling. If
anyone has one of the IDA "Webber" type manifolds, I would appreciate it
if you would provide me two measurements. 1.
The vertical distance from the block-mating surface of the manifold to
the center of the opening of the intakes of the manifold - looks like it
might be 2-3 inches. 2.
The distance from one of the rear center block attachment bolt holes to
the front surface of the front of the manifold - should be on the order
of 8-10 inches. Thanks Ed. Ed
Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
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--
Jim Sower ... Destiny's Plaything
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T
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