This is my feeble attempt to illustrate how the stock Mazda
intake manifold works without benefit of real animation.
The manifold works in two modes. A low speed dynamic chamber
mode and a high speed simple tuned runner mode.
The rotary engine fires once per revolution per rotor. So too does
the intake port open once per revolution per rotor.
In a two rotor engine this happen twice per revolution 180 degrees
apart. Therein lies the possibility of taking advantage of
this fact.
It is convenient for the purposes of this description to consider the
high pressure portion of the air waves in a manifold as a rubber ball.
In many ways it acts like a rubber ball as it has elastic
properties so to speak. It will compress somewhat when it impacts
an obstruction and rebound.
I will attempt to describe the dynamic chamber mode first.
Starting in the upper left of the illustration a ball of air
has impacted the Front Rotor intake port that has just closed.
the ball of air is moving at the speed of sound as the port is closing
and therefor it has inertia and kinetic energy. As the port closes
the ball of air is forced to stop and the kinetic energy
is almost completely converted into potential energy in the
ball. This compresses the ball and it is about to rebound up the runner
pipe.
The ball travels at the speed of sound and it has just enough time
to speed right past the air intake pipe on its way to
the Rear Rotor port. When it gets to the rear rotor port
it finds the port just opening and it continues on in to the engine.
At this moment in time half way between the two ports
where the intake is located the pressure is a minimum and there
is a larger inflow of air. BTW Air never stops flowing into the
manifold but the rate of flow does fluctuate synchronized with
the RPM suggestion that that part of the manifold can be tuned
as well.
Due to the fact the ball always travels at the same speed
this situation in theory only happens at one specific RPM.
For the Mazda manifold this RPM is on the low side around
3000 RPM. As the engine revs higher the effect decreases.
The balls bounce back and fourth from the front rotor port to
the rear rotor port.
**************************************************************
Next I will attempt to describe the second mode I call
the simple tuned length runner mode.
We now have twice the number of balls to work with as the
engine approaches twice the RPM.
Starting on the upper right of the illustration one ball
at the just closed Front Rotor port is just getting ready
to launch itself back up the runner. A the same time
there are another two balls about to bounce off the intersection
of the runner and the inlet pipe we will call the "T".
Air balls bounce every time they encounter any major
discontinuity in the manifold.
A another ball is just entering the engine at the Rear Rotor
port that just opened.
In the next illustration down, two balls are half way between
the T and the ports. One moving in one direction and the other
moving in the other direction.
In the bottom illustration one ball is entering the engine
as the port opens and the other is getting ready to bounce
as the port closes.
The point is the balls DO NOT bounce from port to port.
They bounce back and fourth between port and the T.
Is this clear? Are there any questions?
Paul Lamar
Hi Paul,
How about this for a thought.
In order to prevent the ball from rebounding up the tubes again you could put
reversion cones in front of the port. That would trap the rebound air incoming
and also accelerate the air as it flowed past the reversion cone. I have seen
it used in exhaust systems in off road racing applications. That killed the
shock wave exiting the pipe. Do you think that might work?
Also, I do not know what bearing a turbo charger would have on this set up but
would the impact of rebounding air cause a greater increase in charged air
because of this? A great topic. I use the reversion cones in all of my exhaust
apps but never have used one in the intake.
Doug Mueller'
RX-6 13BT
N900DM
Henderson,Nevada
I don't have a clue about the reversion tubes. I know Mazda thought enough
about the dynamic chamber to use it with the turbos. Probably for good
BSFC at 3000 RPM with low boost when the car was cruising down the road.
Paul Lamar
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