Variable Length Intake

[Birel99]

if that return wave gets back just as the valve is closing how does it suck more exhaust gas out of the cylinder? does it reflect off the cylinder wall?
this is what we do with the 2 strokes but we use the wave to put fuel that may have spilled out the exhaust port back in, oppesed to suck more exhaust exhaust gas out. for the variable length of the exhaust are they just adjusting the diamiter of the pipe or the length? are some systems continuasly adjusting?
thanks,

[Jersey Tom]

I would imagine it works by just having a pressure differential.. low pressure (from reflected wave) on the outlet of the exhaust valve and higher pressure (and probably still some momentum) on the inside.

For the intake side, the idea would be at IVO, a negative pressure wave goes up the intake runner to be reflected down as a positive pressure wave and force more air into the cylinder before IVC. However, as IVO is usually some degrees before TDC I don't see where you'd be getting the negative pressure from.. whereas with the exhaust opening there's still a substantial amount of pressure in the cylinder after the power stroke I can imagine wave propegation.

Thus, exhaust tuning is where its at.

[Birel99]

so for the dimentions of the pipe, its were the expansion chaimber is located to the valve. like, the further away the diamiter increase is the longer it will take for the wave to reach it so the later it will return to the valve= a lower power band, and the closer the faster the wave reaches the faster it gets back and the higher the Rpm power band. does the "expansion" chamber in the exhaust pipe SIZE have anything to do with the speed of the returning wave?
thanks,