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.



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  )
   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


  Thanks - that helps a lot. I amend my opinion (not that it bears any
  weight ) concerning direct injection at the oil injection hole; it
  appears that as the exhaust port closes, about 40% of the included
  volume of the intake is ahead of the oil injection hole, and the air
  inflow might very well cause the mix to be richer around the leading
  plug.

  I'll shut up about this now.

  Victor Roberts





  Hello Victor,


  I'll give it a try too. We use these numbers:



  Mazda Factory Peripheral Port

  IO 86° BTDC
  IC 75° ABDC
  EO 73° BBDC

  EC 65° ATDC




  To define a bit more the opening and closing events look at it this
way.
  The leading apex seal opens a port, while the trailing apex seal
closes a
  port. That applies to both, the inlet and outlet ports.

  Looking at this scenario, from TDC at combustion the [rotary] piston
  travels around
  until the leading apex seal comes to the edge of the outlet port
when the
  outlet begins to open. Using above numbers this is at 73 deg. BBTC.
When
  the leading apex seal comes to the other side of the outlet port the
port
  is fully open.

  The blow down occurs over the next stroke of generally 180 degrees
minus
  the early opening of the inlet port which happens when the leading apex
  seal of that same chamber comes to the inlet port at 86 deg. BTDC.
  This is
  73+180-86 = 167 degrees later.


  When the leading apex seal crosses the other side of the inlet port it
  will
  be fully open and both ports, outlet and inlet, are fully open. This
  condition exists until the trailing apex seal has passed over the
outlet
  port and closed it at 65 deg. ATDC. The beginning of closing is a bit
  earlier.



  The duration of both ports being open is between IO at 86 deg. BTDC
  and EC
  at 65 deg. ATDC or over 151 degrees. On the racing beat J-Port the
  duration
  is IO at 115 BTDC to EC at 57 ATDC = 172 degrees. For overlap only
these
  two numbers count.



  IC determines the degrees of chamber filling in connection with rpm as
  well
  as IO due to its size needed for breathing.  EO should preferably be
  later
  for more expansion but due to its necessary size it sets the
position and
  therewith the timing of EC as well.



  Due to these restrictions side ports are being used that however have
  higher flow restrictions.



  I hope that helps.



  Rolf


 You defined opening and closing in the same way I have understood them.
 The apex seal entering the port area is opening of the following
 chamber, and completing transit is closing of the leading chamber.
 Therefore, opening of the following chamber occurs prior to the closing
 of the leading chamber. When the apex seal in in the port, both leading
 and following chambers are open. One shaft revolution later, the
 following chamber is still open as it's trailing apex is now in the port
 and in the process of closing..
  Port opening occurs before port closing.
 I am easily confused by top and bottom and before and after, so I
 referenced all events to TDC and tried to follow them around beginning
 from the top.  So TDC can be represented by 0 or 360, and BDC is
 represented by 180.
 If we represent all events as ATDC, we get the following:

 EO 73° BBDC  = 107 ATDC  (180-73)
 EC 65° ATDC   = 65  ATDC

 IO 86° BTDC  = 274 ATDC   (360-86)
 IC 75° ABDC = 255 ATDC  (180+75)

 This has the ports closing before opening. Confining our discussion to
 pports, according to our agreed definitions this cannot be true. The
 duration of the intake or exhaust is 360 degrees PLUS the rotation
 required to transit the port.
 I apologize for continuing, I was going to let it drop as Paul's last
 post gave me the info I needed, but unless you can show me an error I
 continue to believe the port timing charts to be wrong.

 Victor Roberts


 Hello Robert,

the answer is that a 4-cycle operations happens over 720 degrees.

Best is to think of a reciprocating 4-cycle engine. I trust it makes it
easier to understand.
Per your distinctions of angles lets say we start out at TDC at firing
when
the power stroke begins and call that 0 degrees and count from there
as you
did.

EO 73° BBDC  = 107 ATDC  (180-73)    (*this is correct*)

EC 65° ATDC   = 65  ATDC (*this is a rotation later*,* should be 425
deg.*)
From EO at 73 deg. the piston goes to 180 degrees and then to 360 degrees
and then travels another 65 degrees until the EC happens. The exhaust
valve
is open all that time.
EC is at (360+65) 425 deg. Valve opening of outlet is over (425-107) 318
deg.

IO 86° BTDC  = 274 ATDC   (360-86)  (*this is correct*.)

IC 75° ABDC = 255 ATDC  (180+75)  (*this is the second rotation,
should be
615 deg*.)
From IO (at 86 BTDC) = 274 deg. the piston goes to TDC then to BDC and
then
travels another 75 degrees until it finally closes. The angular
position is
(360+180+75) =
615 degrees. Duration of IO is (615-274) 341 deg.

The inlet is a bit longer open than the outlet.
Between outlet open and inlet open we have (274 - 107) = 167 degrees.
(close to one stroke of 180 degrees, the blow down).
Overlap when both ports (valves) are open is (IO - EC) (425 - 274) = 151
deg.

I could provide a relation between port lip location and timing
values. But
usually one can't or rather does not change that anyway. It does involve
some calculation and I rather not go there as it is the realm of engine
designers. P-Ports cause limitations in port timing.

Regards
Rolf




Please put aside the timing chart.
Let us observe a port transition.
Begin with an apex between the spark plugs.
Rotate the eshaft so as to move the observed apex toward the exhaust
port. As we proceed, we reach TDC (0 degrees) and continue rotation
until at some point the apex reaches the exhaust port - we call this EO,
(exhaust open). DO YOU AGREE that EC (exhaust close) has not yet
occurred in this rotation?
As we continue rotating, we pass the center of the port, and the angle
ATDC is increasing. Continuing, we reach the other side of the port, and
we call this EC, exhaust close. Granted that it is a different chamber
that is closing, but this the shaft angle that will close the original
chamber on the next rotation.
If EO occurred at some angle, and EC occurs LATER in the rotation, how
can the angular notation of EC be a number smaller than that of EO (
both expressed as ATDC) ?

As the the suggestion that the duration of either port opening is less
than 360 degrees, consider the following:
An apex is in the middle of a port, so the chamber following the apex is
open to the port. Rotate the shaft one revolution, and the following
apex is in the middle of the port, and the same chamber is, and has been
continuously open to the port. Additional rotation is required to close
the port. Therefore, the duration of the opening is 360 degrees plus the
rotation required for the seal to transit the entire port.

Victor Roberts

Forget all this port timing stuff. It is too confusing and a waste of psychic energy.
Think of it as a jet engine. Air comes in.... is compressed and explodes
in more or less a continous process.
Nothing really  opens or closes in the piston engine analogy.

Paul Lamar