Paul Yaw wrote:

The duration of the intake cycle from TDC to BDC is 270 degrees at the
shaft, so you start with 270.  The intake always closes after BDC, so add
that number.  If the engine is peripheral, or bridge, the port opens before
TDC.  In this case add the number.  If the motor has conventional ports they
open after TDC, and so that number should be subtracted.

Example:

US Model First Generation RX-7

IO 32° ATDC
IC 40° ABDC
EO 75° BBDC
EC 38° ATDC

270+40-32=278

Mazda Factory Peripheral Port

IO 86° BTDC
IC 75° ABDC
EO 73° BBDC
EC 65° ATDC

270+75+86=431

The exhaust duration is determined in the same manner. This should keep
Archie up nights for a month.

PY

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