OK, I'm not sure how I feel about this.  It is hard to look at this objectively when I
have spent my entire adult life considering intake flow velocity and how to keep it
UP due to the demads of carburation.  I THINK that I interprete Taylor to mean
bigger is better, but only up to a certain point. AH, the devil is in the details and the
only way I see to solve this is to experiment - on my list of things to do when I get
the airplane flying.
   However, no one has addressed exhaust gas dilution and how the large ports
affect low speed/rpm operation - do not underestimate the importance of this if you
are running a fixed pitch prop.  The engine has got to idle in order for the landing
task to be performed safely.
   At low rpm the exhaust still contains enough high pressure to backflow into the
intake since both the inake and the exhaust are open at the same time (overlap).
This causes all kinds of problems such as lack of oxygen in the intake charge, high
levels of CO(??) which tend to put the fire out, decreases the low pressure of the
intake, and increases intake temp.  I've probably forgotten something important
here, but you can see the problem.
   As stated above, large intake pipes means low velocity at these low RPM's.
Small intake pipes mean higher intake pipe velocities and pressures - these higher
velocites create inertia in the intake charge which blow past the exhaust leakage
and maintain the low pressure of the intake port - these actions help to decrease the
negative affects of exhaust dilution.

Ken Powell

The overlap of the periphery port and the bridge ported rotaries is not a factor in very low speed performance. The driver has a habit of letting the clutch all the way out just as soon as the car starts moving. This should be the worst case for an overlap problem. There is no problem. The car just drives away without protest, with a 2:1 first gear and a 411 rear gear. It shouldn't, but it does. Under 500 RPM is my guess. It will only take a hint of throttle at that speed but it does work just fine. The bridge port is not quit as nice as the periphery port because the port closing is actually later than the periphery port, but they both run fine very slowly with light loads. Idle
(no load) for both is 2000 RPMs but even that can be slower, it just sounds like hell.
Lynn E. Hanover

I would like to point out that the prop RPM with a 2.85:1 PSRU ratio 
and with a 2000 RPM engine idle is only 700 RPM. 

With Ken's 2.95:1 belt redrive it is only 677 RPM which must be much
appreciated by Ken while maneuvering his Coot amphibian in the water.
 
Paul Lamar
 
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