Street Ryderz
Well-Known Member
Why does port durations matter, what do they tell you? What does knowing the durations tell us?
First, it should be clear to anyone who has made even a cursory study of the various two-stroke engines' port timings that no close correlation between these timings and engine speed exists.
Second, it should be equally clear that the basic function of these ports - which is to permit a volume of gases under pressure to escape confinement, is not solely dependent upon time.
Time is required, obviously, but the process is one that also is sensitive to area. In other words, at any given pressure differential the time
required to move a volume of gases through a port in the side of a cylinder wall will be mostly a function of the port's cross-sectional area.
Thus, it is not possible to treat with timing alone when planning the porting in a two-stroke engine; you must find the
combination of time and area that will permit complete passage of the gas volume at hand.
First, it should be clear to anyone who has made even a cursory study of the various two-stroke engines' port timings that no close correlation between these timings and engine speed exists.
Second, it should be equally clear that the basic function of these ports - which is to permit a volume of gases under pressure to escape confinement, is not solely dependent upon time.
Time is required, obviously, but the process is one that also is sensitive to area. In other words, at any given pressure differential the time
required to move a volume of gases through a port in the side of a cylinder wall will be mostly a function of the port's cross-sectional area.
Thus, it is not possible to treat with timing alone when planning the porting in a two-stroke engine; you must find the
combination of time and area that will permit complete passage of the gas volume at hand.
