Jerry Hey wrote:
I spent about 5 hours trying to chop down the 2 inch 180 degree
sweep.
The plan was to cut a section out of the bend which would
cause an
out
of round condition which I would repair by welding in material
and
then
grinding to get back to round. It started out well and I soon
had
the
two inch runner hugging the top of the engine. The problem
came
when I
could not quite maneuver the tig torch far enough into the
tube to
deposit material as far back as needed for fairing out the new
radius.
It would have been so easy to do with J & B weld (J & B
whiskey
would have also come in handy) but the last step of welding
the two
halves back together prevented that. I will spare you the
details.
I
abandoned the effort as a no go.
So where to go from here. I see three possible solutions. One
is to
use a smaller diameter intake runner. The 1.5 o.d. runner has
a 2.5
radius and would fit nicely. There would have to be a reducer
with
an
internal taper to connect up soothly with my 2" o.d. throttle
bodies
but that is not a big deal. The question how does that size
runner
effect performance? I do like getting the fuel to the cool
side.
The second possibility is to use the off the shelf 2 inch
bends and
lean them over. As you said, I only need to lean them 20
degrees
to
get clearance. However, to lean them even 20 degrees, I have
to
either
cut down or relocate the water pump. I have wanted to cut
down the
water pump anyway just on esthetic principles. But this
solution
may
not apply well to other installations especially those that
need to
lay
down the runners a lot further.
The third possibility is the Russell Manifold. It is
starting to
look
better all the time.
In looking for a solution, I would like to choose one that
works
for
every application and not just mine.
To me, if the 1.5 inch runners will work, then that is the
way to
go.
If not, then the Russell manifold would be the second choice.
I do want to ask about the possibility of a carbon fiber 180
degree
bend. I am thinking of something we can clamp the straight
aluminum
legs into. Is this feasible?
Jerry
I agree with you on the Russell manifold and I am doing further
work
on it.
Hopefully I can get the plenum box straight up and down. Hang on
more to come.
BTW To calculate the center line length of a 3 inch center line
radius bend
multiply the angle by .0524. For an example a 45 degree bend
center
line
length would be 2.356 inches long.
BTW jerry cut down the length of the TB's as every little bit
helps.
You don't need the hose barbs on the the prototype since the
manifold
is under vacuum almost all of the time. All you need is 5/8 of
an
inch
hose barb.
Paul Lamar
This is it. Uses a 6.5 by 4 by 4 Zero box with alternator
flapper.
Bends 45, 180, 90, degree front tube.
Bends 20, 90 degree back tube.
Move the starter up as far as possible.
Adjust the length by moving the whole works closer or further
from the engine. You can also adjust the length by moving the
plenum forward. Moving it aft is not possible.
The neck bone is connected to the back bone and the back bone is
connected
to the hip bone etc., etc., etc., so don't make any other
changes.
Everything fits under the stock cowl.
Current length is about 20 inches.
Paul Lamar
This is a breakthrough in intake manifolds. we have been fighting
over
the
top for years. All made possible by the P-port. This will
probably even
fit in a Lancair 360.
Thanks Russell.
Paul Lamar
It is beautiful but.....some things I still worry about. The
plenum
box seems too small. Ram air blasting into that tiny box is going
to be
extremely turbulent. Is this bad? I don't know. The rule I have
heard
is the bigger the better when talking about intake plenums.
There must be a thousand articles posted on the internet about
intake
tuning. To generalize, long, skinny runners are better for low
end
torque and fat, short runners are better for max hp at high rpm.
Nobody discussed big, fat, long runners. All this kind of talk
is so
vague it is impossible to apply. Is our aircraft operation "high
rpm?" Not according to Jim Mederer who a couple of years ago
suggested
very small p ports and tiny runners for a 6000 rpm engine.
Here is another rule I read today: the intake runner diameter
should equal the port diameter. Does that mean our intake runners
should be 1.5" i.d. which is the size of my p port? My 1.5 port
is
predicted to be able to flow adequately up to 8,500 rpm. Hmmmm.
1.5
i.d. runners would be a piece of cake to install on either side of
the
engine.
It is almost pointless to talk about runner length. If the runners
cross over the engine they are going to be LONG.....and if they
stay on
the hot side, they are going to be SHORT. And whatever length they
are, they are only tuned for a certain rpm. If you want to go
faster
or slower, the intake is not going to be tuned to the job. How
critical is intake length? At the drags, it might make all the
difference but I doubt it is that critical for our medium rpm
engines.
I believe Tracy uses a smaller intake runner, or at least he used
to.
He uses little exhaust pipes too and a restrictive muffler hanging
out
in the breeze. But he is gong 200 mph. I think this is good
news.
Jerry
Well if you have room a larger plenum would be possible.
Mostly taller. IMHO you don't need it. Have you seen the plenum on
a 3rd gen
or
stock 3 rotor?
The runner length and size shown here is roughly what
the Lemans engine had. Are you going to go on what some piston
engine
weenie says or are you going to go with what the Mazda engineers
developed
for the 4 rotor to win Lemans ? :)
An aircraft engine is not like a car. The RPM range is less than
a 1000. Static to max speed. A car RPM range for a car is 1000 to
9000.
Write this down and paste it over your work bench. I am getting
tired
of saying this. Don't make me send you the old messages on the
subject. :)
Think of how much faster you will go than Tracy. If small pipes are
the hot
tip why are you building P-ports? Allan Tolle went 238 MPH in the
Sun 100
with P-ports and about the same size pipes. He also had the fastest
time
to climb to 3000 feet beating all comers including jets.
Paul Lamar
Paul
I hear what you are saying. I don't understand completely why you
bring the
LeMans racer engine up a lot. Wouldn't a better example be found in
the
length of the third high speed manifold, that activates at 7250 rpm
in the
RX-8 and tweak it from there? That is the state of the art isn't it?
To try
to understand better I just spoke over the phone with the LeMans
racer's
intake manifold designer. As everyone know it was designed with
adjustable
length manifolds, which change length according to the engine rpms to
provide the best tuning for that particular engine for those
particular race
parameters. The manifold itself created a fairly straight in laminar
flow
with no rammed air included. It had crude air filters made from a
piece of
sponge in rather small boxes.
I happen to agree with you to use larger pipes to decrease air flow
skin
resistance and understand every twist and turn creates some
resistance IF
they are too abrupt. But adding the effects of rammed air in the
manifold
changes the environment doesn't it? The sized length for a desired
rpm
remains set but adding a boost increases the manifold pressure a
few inches
with a good design like you have created. A balancing act is probably
happening. The only moment the intake plenum experiences a vacuum is
when
the intake port opens. If any of my experience mixing gas and water
through
venturis holds is applicable, IMHO I'd venture the balance point
would be
licking at the lips of the bell mouths. In an ideal situation Jerry
could
run the engine with temporary adjustable intakes lengths. Max power
or max
economy are the two extremes right? Without testing the engine on
some sort
of dyno, all theory, including mine, is academic:)
Do you have any pictures of Allan Tolle's intake manifold? Sounds
like his
system is a good proof of the pudding for the max power thinking. He
probably made it over 10 years ago. His thoughts and opinion would
provide
food for thought.
Doug in Japan
The beauty of the Leman engine is it generated a record amount of NA
HP per
rotor over a wide range of intake manifold lengths. Not only that it
had
outstandingly low fuel consumption. No Mazda tuner in the States or
else
where in the world has been able to equal what Mazda did with the
Leman
NA engine. Here again is all the data for the new guys. You need to
divide by
two for the 13B P-port version.
At 6000 RPM Jerry is looking at close to 240 HP. That will also be
the best BSFC point. A good cruise RPM number with a cruise prop.
To scale this rotor housing drawing the throcoid curve hump to hump
is six inches.
That makes the pipe diameter slightly under 2 inches.
The fixed pipe length is 9.8 inches to the 45 degree curve and another
2.7 inches to the rotor face. The correct adjustable portion of the
pipe length
at 6000 RPM 175 mm or 6.9 inches. Adding this to the fixed pipe
length is 19.4 inches
overall. So Jerry engines is tuned to around 6000 with the 18 inch
version (20
inches overall) of the Russell. Checking the HP curve that is 120 HP
or rotor
or 240 HP. BTW If we could figure out how to shorten the Russell
another couple
of inches we could get even more power.
A fixed intake length runner has the effect of flattening the HP curve
compared to the steeply rising variable length intake runner HP curve
of the Lemans engine. Lets us figure out what the HP of Jerry's engine
will be at 7000 RPM.
One Newton is .2248 pounds and one meter is 3.28 feet.
Therefore N-meter to foot pounds conversion factor is .737 I think.
At 7000 RPM Jerry engine, with a fixed 20 inch length intake pipe,
will be generating
270 N-meters (540/2) or about 200 foot pounds of torque. Way down
from peak torque.
Using the old standby formula for HP yields 200 x 7000 / 5252 or 266
HP
with a top speed prop. BTW for all you guys that think torque is the
be all and end all that is 570 foot pounds at the prop with a 2.85:1
gear box. With a variable length runner Jerry's engine would be
generating close to
300 HP at 7000 RPM. 300 HP would probably be enough to tear the fabric
off a Tailwind :)
It will be interesting to see how close Jerry comes to these number.
Vance, Rolf or anybody else please check my conversion and
calculations.
Paul Lamar
Here is the calculated HP curve of the 18 inch fixed length Russell.
It is over 230 HP from 5900 to 7500 RPM. Actually with the ram air
scoop
the HP numbers on the top end will be slightly better than this as
the RAM air pressure is proportional to top speed squared.
You will not get this HP in the air unless your RPM matches these
numbers
at the top speed of your airplane. Therefore the prop pitch is
important
so it would be nice if Jerry or anybody else for that matter with a
tuned
intake manifold had either a ground adjustable or constant speed prop.
Allan Tolle told me he had several fixed pitch props. One for top speed
in the Sun 100 race. One for the time to climb contest and another for
cross country cruise.
I would say this manifold is very well matched to a 2.85:1 gear box.
Again airplanes do not need HP at anything less than static RPM.
Here is some piston engine data on pipe diameter and length.
Smaller pipe diameters at a given length DO NOT broaden the torque
curve.
This data clearly shows that. Smaller pipes merely reduce the HP
obtained
by shifting the tuned length down in RPM. The vol. eff. AKA torque
remains
more or less the same. HP however is torque TIMES RPM so the HP is
drastically
reduced. First and foremost AIRPLANES FLY ON HP AND NOT TORQUE!!!!
If you want a broad torque and HP curve use no pipe at all and lose
35 HP! You will also lose about 15% in the BSFC department because
the vol. eff. is also reduced.
Paul Lamar
Thanks Paul. I do intend to build the Russell intake using two inch
tubes. I am very glad to have the analysis you just provided.
Jerry
After studying some of those curves smaller pipes appear to NARROW the
torque band. You can see it in both charts. What that means is a larger
than 2 inch pipe tuned at 6000 RPM in length would have a broader torque band.
I suppose Mazda decided 2 inch hole was about as large as they could stuff
through the rotor housing wall :)
Paul Lamar
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