Date: Sun, 31 Jan 1999 02:06:15 -0800
From: Paul <rotaryeng@earthlink.net>
To: z <rotaryeng@earthlink.net>
Subject: Dynamic Chamber Intake manifolds

Paul Yaw wrote:

Tracy Crook wrote:

 Since it is hard to fabricate an exhaust system that is both 

tuned for best

power AND quiet in an aircraft installation (here we go, another 

long debate

:-) ),  I think we are working with the exhaust pressure pulse, so 

the

shorter runner length would apply.

A set of generic headers collected into a piece of 2.5" tubing with 

even

a turbo style muffler will reduce back pressure a great deal.  I think
that the second pulse caused by exhaust backpressure would be pretty
much non existant even with the systems that you guys are running.  I
have no proof, this is just an educated guess.  If you look at the
pressure plots, the exhaust induced peak is quite small, and the stock
exhaust system is VERY restrictive.  The hot ticket would be to 

utilize

the pressure peak that occurs at intake closing because it is MUCH
stronger.  This of course will result in a proportionally stronger
pressure wave.  It also means about 50 yards of intake manifold.

The reverse flow is the reason that bridge or peripheral ported 

engines

do not idle smoothly.  Keep in mind that the clearance volume (the
volume at TDC) is full of exhaust gasses that are pulled through to 

the

next intake cycle.  This clearance volume accounts for 10.6% of the
total volume.  (Volume at BDC)  When you think of it that way it seems
pretty scary.  That is one of the reasons that bridge and peripheral
engines make so much more power.  Having a large overlap period,
inertial, and pressure wave scavenging can be used to replace these
exhaust gasses with fresh intake charge.

 It should also be remembered that the length  in Paul Yaw's 

message is

the TOTAL length of runner between rotor 1 and 2.  That means the 

runner

length from each port to the DC would only be about NINE inches 

long.  And

remember that there are a few inches of runner length between the 

port on

the side of the engine block to the actual port opening to the 

rotor

chamber.  The length of the DC itself also counts in this setup.
Considering all this,  I'm beginning to think my existing manifold 

runners

are  TOO LONG! :-)   I can't wait to see how that little composite 

manifold

on my test stand will work.

No, that is the length of the runner for EACH rotor.    Those stock
manifolds are REALLY long.

On the topic of Everett's manifold, his was a classic tuned pipe, 

not a DC

design.  According to him, 4 tubes (even of the perfect length) 

going to a

side-port engine did not work well on the dyno for a 6000 rpm 

design.  His

explanation was that the velocity was too low when split between 

the two

pipes (per rotor).  This was his primary reason for going to 

peripheral

ports.

That is way off base.  Velocity is determined by the rate of change of
volume of the working chamber, and inlet cross sectional areas.  The
side port motors make less power because they don't flow nearly as 

well,

and unless thay are bridge ported, they have almost no overlap.  This
theory illustrates a VERY poor understanding of flow dynamics.

Paul Lamar wrote:
Use two tapered intake pipes near the ports and make them bigger.
Paul Lamar

Tapering the pipes will cause them to resonate at a higher frequency.  

I

found this stated in literature years ago, and thought it seemed
impossible, so I did some testing and found this to be true.

Paul Yaw

Sorry about the draconian editing guys. I just try to keep
the new stuff. 

Lets send some manifolds to Paul Yaw for testing.

Paul Lamar
 
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