So far you guys have shown me no data to support your contentions.
I guess I am going to have to scan yet many more graphs from Taylor to
convince you guys. It would be better if Tracy took some of that $500
he has and bought the two volume set of Taylor's bible of engine
design
books. Would save me a lot of work :-)> When I would go up to see
Everett
Hatch years ago he would carry his Taylor around with him
where ever he went. We would go out to lunch and he would quote
various passages. I miss the guy.
Paul Lamar
Paul,
What does Taylor mean by intake tract diameter? runner AND port, or just
runner?
Extend your argument to its extreme and use a runner pipe of infinite
diameter. This will result in a very low velocity in the runner (zero).
You
now have a very low VE (according to your data). Velocity DOES matter.
The lemans engine has nice numbers, peak torque, min BSFC, and probably
max
VE around 6300 rpm or so. Great operation between 4000-7000 rpm. Perfect
for
airplane use (with a variable pitch prop :-) However, I want to see what
the
torque curve looks like below 4K. Just convince Ken to cut his housings
and
put in those variable timing/area ports, and the problem will probably
go
away. No debate on any of this.
I'm too tired to argue any more. I have more points I can make, but no
energy to make them. Maybe I will recover by Sunday. I need a jack
hammer
(for the chimney not your head :-).
Monty
Obviously infinite is out of the question. If it was a piston engine
it would be the diameter of the piston. If it was a Wankel it would
be a pipe dia. of equivalent area of the face of the rotor.
There were some piston engines built with rotary valve cylinder heads
that approached this ideal. The sealing problems were never solved.
Paul Lamar
If velocity does not matter, then why should the pipe be only as big as the
port area? Why not make it larger and get even less velocity, and skin
friction? I think your Idea of impedance coupling may be on the right track.
Where is the energy to create the pressure waves coming from? The piston or
rotor initially gives the negative pulse (a pressure differential analogous
to voltage, an AC sinusoidal voltage source shifted above zero to be more
specific). The air starts to move (inertia here is analogous to inductance)
and must overcome the pressure drop due to flow loss in the runner
(analogous to resistance) Capacitance could be thought of as the volume of
the runner or plenum. The one thing missing here is current or amperage. In
that term (really a mass flow in this case) you will find; guess what?
VELOCITY (m dot =V*A). Designing the ideal intake tract is the same thing
electrical engineers do, designing a circuit with the least impedance, (a
fancy form of resistance for AC circuits) it will have very low impedance
for a SPECIFIC range of frequencies. In this case the frequency is
determined by RPM. If you neglect velocity in your quest and build massive
ports and massive runners, you will have created a very low impedance at
high rpm. At low rpm the impedance will be greater. One would think that the
larger port and runners would have less resistance to flow and this WOULD be
the case for a CONSTANT flow (the same as a DC circuit) but it is not the
case for a periodic flow (an AC circuit) You cannot analyze an AC circuit
with DC techniques. These are not perfect analogies by any means, but I
think they have some validity. The chart illustrating varying diameter with
constant length is really of little use, because the smaller diameter runner
will naturally work better at a longer length at low rpm. It will likewise
suffer at higher rpm.
The case with ports the size of the piston/rotor, and a runner sized
accordingly would be ideal for max high rpm power. But your data shows that
the smaller diameter runners reach their peak efficiency at lower engine
speed. The larger ones at higher rpm. It is no use to put huge ports and
short large diameter runners on a garden tractor engine that never sees over
3000 rpm. In fact I bet it would be detrimental to VE. But the only way to
know for sure is to build it and see.
Monty
I'll give you the last word :-)>
Paul Lamar
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