ive just read this on tt net,its got to be the best explanation of my good old goose honk:=
The recirculation valves are modulated by vacuum signal from the intake plenum. When you boost 10PSI at WOT, the intake pressure matches the vacuum control pressure and the valves remain closed. Let go of the throttle and the intake pressure starts to climb because the turbos are still spinning, but on the other side of the throttle plates a vacuum immediately develops. Suddenly, there is a 20psi pressure difference between the intake and the recirc. valve control lines...so they open.
What is happening is that when boost comes on at partial throttle, the pressure difference between the sides of the throttle bodies causes the recirculation valves to open, altering the overall geometry of the intake tract.
The noise, however, does NOT occur because of the valves 'fluttering' open and shut. It happens because the POP charger allows a smoother, faster flow of air than the stock airbox did. That incoming air blows directly over the outlet ports of the recirc. valves and sets up an harmonic resonance in the intake tract through those ports.
Ever blow across the opening of a beer bottle? You get a noise VERY similar to the one you're hearing in your intake, because the same principle is at work here.
When you give it WOT, there is no real pressure difference across the throttle plates and the recircs are shut...no noise. (Just like if you were to break the neck off the bottle and then blow across the opening...without the enclosed volume behind the port, there is no "chamber" in which to set up a resonance.)
ive just read this on tt net,its got to be the best explanation of my good old goose honk:=
The recirculation valves are modulated by vacuum signal from the intake plenum. When you boost 10PSI at WOT, the intake pressure matches the vacuum control pressure and the valves remain closed. Let go of the throttle and the intake pressure starts to climb because the turbos are still spinning, but on the other side of the throttle plates a vacuum immediately develops. Suddenly, there is a 20psi pressure difference between the intake and the recirc. valve control lines...so they open.
What is happening is that when boost comes on at partial throttle, the pressure difference between the sides of the throttle bodies causes the recirculation valves to open, altering the overall geometry of the intake tract.
The noise, however, does NOT occur because of the valves 'fluttering' open and shut. It happens because the POP charger allows a smoother, faster flow of air than the stock airbox did. That incoming air blows directly over the outlet ports of the recirc. valves and sets up an harmonic resonance in the intake tract through those ports.
Ever blow across the opening of a beer bottle? You get a noise VERY similar to the one you're hearing in your intake, because the same principle is at work here.
When you give it WOT, there is no real pressure difference across the throttle plates and the recircs are shut...no noise. (Just like if you were to break the neck off the bottle and then blow across the opening...without the enclosed volume behind the port, there is no "chamber" in which to set up a resonance.)
jay