Chuck wrote:

Here is a photo of my plenum chamber with 180 bends inside to take advantage
of the dynamic charging effect. I tried enlarging the openings in the bends
but never did get as much power as with the simple bell mouths made of
nylon. I took the bends assembly out and put the bells back in.
I never did understand how this was supposed to work. It looks like the
pulse charge would want to go into the box and out through the throttle
butterfly rather than into the other rotor. Perhaps my runners are too long,
but it would be really tough to make them any shorter, no clearance at top
of engine.

Chuck Dunlap

So why does it work for Tracy but didn't for Chuck?
Could it be because Tracy uses ram air with a short narrow path to the inputs of
the dynamic chambers? Chuck, on the other hand, had a huge plenum (allowing in and
absorbing the pressure pulses instead of passing them on into the other runners)
between throttle body and ends of dynamic chambers.

Tracy?

Finn

Finn, I gave you the wrong answer. We will never know because Chuck
and Tracy never had their engines on dyno's. The thing about prop
load is the engine RPM increases until the HP required by the prop
and the HP put out by the engine coincide. There is no way to load
the engine down at RPM's below or above that number to find out how
much HP is available at what RPM from the engine. For all we know Chucks 
Dynamic chamber was working fine at 4000 RPM. Also we will never know 
if Tracy's dynamic chamber is working at the RPM his engine is generating. 
It may be optimum for some other RPM greater or less than 6600. 

Things will get better soon when we get a variable pitch prop. Butch 
tells me any day now. We will need to make a simple dyno however to measure 
the torque at various prop RPM's and prop pitches and calculate
a HP curve. Until that time we are merely guessing based on what 
Power Sport did and what Mazda published in their SAE papers.

I will say it is going to be a lot simpler to tune a simple tuned
manifold to prop requirements than any dynamic chamber design. All 
you need do is adjust the runner length while the dynamic 
chamber depends on way more variables not the least of which is the 
exact design of the chamber itself. I would not be a bit surprised 
if Mazda did not spend millions on the exact configuration. Furthermore 
that D.C. configuration took into consideration the need for low speed torque
in automotive applications which is of no concern to us at all right at
the moment due to the characteristic HP requirements of fixed pitch 
props mentioned above.

Paul Lamar
 
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