Lynn
Your
saying what I want to hear P-port, high intake velocity (smaller diameter
tubes - I thinking about 1.6") and a after considering Tracy's set-up
and Talking to Ian Beadle ( Western Australia) I'm also leaning toward the
shorter inlet tube length.
Of course nothing beats proof of testing.
Speaking to Ian (he's into electronics) he suggested ( If I understood
him correctly) that the sine wave of the exhaust pulses are shorter as the
RPM goes higher (makes sense), so the intake length needs to be
shorter.
I was always under the impression that the shorter manifold was
for torque and the longer for HP - but as they are
inextricably linked (HP=TxRPM/5252), what real difference is there, if
any, in relation to aviation needs. Perhaps pulling a few more RPM??
Mind you I'm still working on the single and to get a healthy HP out of
it. I'm hoping to achieve 125HP and maybe as much as 150 hp.
I'm still debating the simplicity of a carby V fuel injection, after
riding the new bike around Australia I now understand the benefits of FI in
relation to economy.
BTW I was hoping you would take a stab in the dark and say 6" to 8"
would be sufficient for the intake tube.
After thinking about two TB's (as you suggested), it adds another
variable to the equation, I've got all sorts of things to consider.
On another point, have you used the steel Bellhousings on the rotary
and are they very heavy!?
George ( down under)
Lynn.
What's your take on the runner length for 6,000? I believe
you add the plenum length to the tube length for the total length, So I
guess the longer/ bigger the plenum the shorter the tube has to
be.
George (Down under)
I was hoping nobody would ask me that until I have tried a few on the
dyno. I need to go back to square one and get out some books, and have my wife
teach me Algebra and Trig again.
The problem in kind of a dumb way is that almost anything will work well
enough to power nearly anything you could want to fly in. Look at the
McCulloch Drone engines. 79 pounds, 72 HP. No inlet tract, no runner length no
air cleaner, no injection, carb a 4" tall length of pipe with a needle valve
stuck through one side and a gas hose through the other. Bolted solid on the
crankcase. Actually very well designed with a built up crank in needle races
needle bearing rods and wrist pins.
Designed to last less than 10 minutes and get shot to pieces during that
time. The stud spacing for the intake tube was the same as an old 6 cylinder
Plymouth carb. So getting one running was no trick at all. So is 4" just right
for 5,500 or whatever those things ran?
I know the props were not very long. Probably not. Maybe 8" or 10" would
have made a bit more HP. Was the square cut end of the tube a lack of
thinking? Or was the vena contracta so produced, there to make a depression so
the lack of a venturi would still get the carb to work. If you put a nice bell
shape on the top it would flow more air but have no differential pressure to
flow fuel. So the unhappy drag of a squared off tube becomes a carb
choke.
The two rotor Mazda (It isn't really a Wankel) is two 4 stroke Otto Cycle
engines running on the same crank, and sharing a iron segment to save weight.
The piston controlled valving feature makes the
intake tune just like a piston port 2 cycle engine of the same
displacement. About 575 CC per engine. So for 5,000 to 7,000 it aught to
look kind of like a good running 500CC single dirt bike engine? And in
airplanes we see whopping big diameter tubes running over the engine and
clamped to a big plenum chamber with a big TB on one end or the other. Enough
induction system for over 500 HP. Just to wring out a paltry 160 (Maybe) HP?
The first good Chevy engine I built was a 302 for a CanAm car. It had a
Crane roller cam and gear drive. It made a wonderful gear howl when it
ran. The intake was Endrel manifold and tubes looking like a pipe organ. Not
very large in diameter, and shorter than others were using. It was a dribble
system like the Bendix systems on Continental engines but even simpler. The
engine driven pump metered fuel to a distribution block and then into nozzles
and into the intake all of the time. There was a line back to the fuel tank
that went through a selector block where a number of return jet sizes could be
selected by the driver to adjust gross mixture.
And I do mean gross. The real smart guys had other ways of tailoring
parts of the band but we didn't. We didn't have a clue. When the car was sold,
the new owner put that little cast iron Chevy on Jerry Mong's dyno and got 575
HP. It was nothing like the big guys had, but in a 1300 pound evil handling
Lola, it was enough to keep the driver hysterical. Waking up at night
screaming, drinking too much. The usual stuff. But those tubes were so small
compared to what others were running. The intake valves were only 2.02" so how
big a diameter was correct. ??? I never found out.
Anyway the runners on our store bought (Daryl Drummond) race engines are
very nearly stock diameter. The very slightly modified stock manifold gasket
is used. The high mid range is important in a race car. The closer you
get to 2,000 RPM of power the better.
This is to have power when a gear change pulls RPM down further than was
expected. If you pull it down too far the time spent accelerating
again would have been saved with a downshift to the next lower gear.
So in an airplane, it is good to have power enough to at least stall the
prop a bit on power up from stopped. Rapid acceleration to lift off with less
time for gusts to upset you. Less time with poor aerodynamic control, and so
on. All the good stuff. So airplanes should have a good mid range although
lower than the race car, and the mid range should be strong. With
increasing power as the revs come up right through cruise to top speed.
So what makes good mid range? runner velocity. More is better. Smaller
diameter is better than larger. Straight is better than curved. And if
injectors are closer to the port, slick and shiny is better than anything
else. The inlet end must be protected by a free flowing air filter, and no
vena contracta at the ends. Bell shapes only, always.
Other things to think about. Without a dyno and an adjustable length
runner system the chances of hitting the ideal length for best top power and a
good mid range, is zero.
But how about this. A log manifold is a convenience so you can run a
single TB and cable system. So two engines are miss tuned by interconnection,
for convenience. How about two smaller TBs? And it is two engines, not 4
engines, why 4 tubes? How about two tubes?
Either with a junction close to the engine or just bite the bullet and go
Pport with two tubes and 2 TBs. Much less space involved, and less complex
with much more power. You can get the length and diameter wrong and still make
more power than a side port engine. Notice Tracy's short runner intake?
Running real well.
More later.
Lynn E. Hanover