These numbers for the Mazda P-port are bogus.
  As Paul has  pointed out, there is an overlap of intake timing between
  adjacent rotor faces.

  When the apex seal is in the center  of the port, two chambers are
open  to the intake. From this  position, after 360 degrees of shaft
rotation  the rotor face  which was just beginning intake before the
rotation would  still be half open to intake after the rotation. The
intake  period  exceeds 360 degrees of eshaft rotation.  Reference
these numbers to after TDC and it becomes apparent they  cannot  be true.

  The intake opening at 86  BTDC is 274 degrees of e-shaft rotation
  After  TDC.
  The intake close of 75 ABDC is 255 degrees After  TDC.
  This gives us 19 degrees of shaft rotation where neither  is open.
  For the exhaust, opening at 73 BBDC is 107 After TDC,  and closing
at 65  after TDC - 42 degrees of shaft rotation  when no exhaust occurs.

  It appears to me that the interior  circumference of the rotor housing
  is about 27 inches; so 360  degrees of shaft rotation is 9 inches.
A  two-inch port opening  then requires 80 degrees of shaft rotation
to  transit, so the  trailing port opening occurs 80 degrees ahead
of the  leading  port closing. The intake period including overlap
is about 440  degrees of shaft rotation.  The exhaust port appears
to be half  the size of the intake, so 400  degrees of shaft
rotation from  opening to closing.

  Tell me where I am  wrong.

  Victor Roberts

  Are you referring to these numbers as being bogus?

  Mazda Factory Peripheral Port
  IO 86° BTDC
  IC 75° ABDC
  EO 73° BBDC
  EC 65° ATDC

  These are typical representations of timing numbers used  in rotaries.
  Notice the similarity to numbers for a "J" bridge  port.

  Racing Beat "J-Bridge Port"
  IO 115° BTDC
  IC 72°  ABDC
  EO 88° BBDC
  EC 57° ATDC

  The numbers used are  started at the nearest of four locations.
  A TDC or a BDC.  This to keep numbers small and understandable.
This is  adequate to lay out  markings to port an exhaust or intake
or lay out  your

  Pport boring location. And  recover overlap degrees,
  All of these numbers can  be resolved while looking at one rotor face.
  The two TDCs are minimum  volume right or left side and two BDCs maximum
  volume
  top (Intake) and bottom (exhaust).

  While it seems backwards, the Pport engines are more  tractable
than the  bridge ported side port engines. Although both have very  little
  torque right
  off idle we could drive the Pport to and from the false  grid with
no  problem where the "J" bridge ported were towed with a small  tractor.
  This to save
  the clutch. A Tilton of course.

  The Madeville modified factory Pport housings had  enormous rectangular
  intake ports and are also quite tractible at low RPM.
  _http://alex62.typepad.com/imsablog/2006/02/mazda_rx7_winni.html_
  (http://alex62.typepad.com/imsablog/2006/02/mazda_rx7_winni.html)
  They ran unmuffled at most locations and even with no back
pressure idled  smoothly.

  The idea that much if any fuel will be lost to the exhaust system
at or  near  cruise RPM is not founded. It is my opinion that when muffled
  and at low
  RPM  exhaust pollution of the intake charge actually helps smooth
out the  idle in the  Pported engine.  Lynn E. Hanover

I understand the BDC and TDC references. I converted them to a common
ATDC in order to make the relationships easier to calculate. Because
of the 3:1 e-shaft to rotor gearing, each face of the rotor requires
360 degrees of e-shaft rotation to pass over any given point on the housing
circumference.

I guess there is a question of what "port open" and "port closed" means.
In my experience with piston engines, "open" means when the valve comes
off the seat, and "closed" means when the valve returns to the seat.
"Overlap" defines the period when neither valve was seated. For 2-stroke
engines, "open" and "closed" refer the transition from closed to
partially open and open to completely closed, respectively.

On a p-port rotary, does "open" refer to  the time the apex seal:
A. enters the port ;
B. clears the port; or
C. some other time?
What event defines "closed"?

For an engine to have a volumetric efficiency of 120%, the intake
must have been charged with pressure greater than 120% of ambient at
the time the intake port closed,  or part of the intake air must
bypass the intake stroke directly into the exhaust. It would appear
most likely that an elevated intake pressure would both charge the
intake above ambient, and force air into the exhaust during overlap,
a period when exhaust back pressure is at it's lowest. Since most of
the operation is at cruise power, it is this condition I am
concerned with.

I ask here because I have attempted to research these questions and have
been unable to find the answers.

Victor Roberts

Here are some diagrams that might help.

Paul Lamar


Victor,
There are a couple of things to keep in mind about the intake charge ina
p-port rotary engine.
One is that the intake tract air flow does not stop. As the apex seal passes
the port, the flow just starts to flow into the next chamber (side of therotor).
The next is that the rotor starts pulling away from the rotor housing when
the apex seal has passed the port. This causes a strong draw on the port and
intake tract. When the intake length is tuned to the right length for the
operating RPM the momentum of the air in the intake pressurizes the side of
the rotor that has essentially stopped expanding, but the port is still open.
This is why you can have 120% volumetric efficiency. The tuning has to be
correct for the RPM to achieve this number. Race piston engines can get better
than 100% efficiency when the stars (tuning) is correct, without supercharging.

Dale Davies