If you want to get into the weeds on how rotaries work, here is the
port timing for many stock and racing engines. From Paul Yaw's web site.
Now closed down.
Notice that the factory Periphery port timing is more modest than the
"J" bridge port timing. So the Pport actually idles and slow runs smoother than
the bridge ported engines.
Port Timing
IO = Intake opens
IC = Intake closes
EO = Exhaust opens
EC =
Exhaust closes
US Model First Generation RX-7
IO 32°
ATDC
IC 40° ABDC
EO 75° BBDC
EC 38° ATDC
European Model First Generation RX-7
IO 32°
ATDC
IC 50° ABDC
EO 75° BBDC
EC 48° ATDC
First and Second Generation 6-Port 13B
Primary
intake (Part throttle/cruise)
IO 32° ATDC
IC 40° ABDC
Secondary
intake (Part to full throttle)
IO 32° ATDC
IC 30° ABDC
Auxiliary high
speed ports (Full throttle above approximately 4000 rpm)
IO 45° ATDC
IC
70° ABDC
EO 71° BBDC
EC 48° ATDC
Second and Third Generation Turbo 13B
IO 32°
ATDC
IC 50° ABDC
EO 71° BBDC
EC 48° ATDC
Racing Beat "Street Port"
IO 25°
ATDC
IC 60° ABDC
EO 84° BBDC
EC 48° ATDC
Racing Beat "J-Bridge Port"
IO 115°
BTDC
IC 72° ABDC
EO 88° BBDC
EC 57° ATDC
Mazda Factory Peripheral Port
IO 86° BTDC
IC 75° ABDC
EO 73° BBDC
EC 65°
ATDC