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