[TonyS9]

The measured air story is total BS/myth. The ECU does not remember air from the past, all it knows is whats happening now. You need to dump the high pressure air so that the air flow measurement is valid and so idle can work. Also that turbo doesn't stall or get stressed. However the latter turbo problems are perhaps minimal, there is no definate evidence that running without dump is a real problem except for idle.

All dump valves are atmostpheric. The air has to go somewhere and the Engine cannot use it (otherwise you would not need a dump). The original one is insulated by lots of ducting and padding in the air filter box. A recirc dump is just as loud as atm dump if you use a cone filter rather than the mfrs air box.

Non-recirc valves are only different in that they have to close for idle, so they have an intermediate pressure that is close too but not atmostpheric, so they may take second or so to settle while the remaining pressure is lost and the MAF reading comes up to drive the injectors properly. It may get a little weak at this point.

Im running a closed breather and having oil leak problems, originally I blamed the dump (correctly) and now have recirc and atm dumps and 2 check valves, however I think I'm getting piston blow past now. I tried running on the track with and without out dump. It doesn't make much difference until you park up, when it needs a few seconds to depressurise before it will idle.

For tuning I wouldn't worry about it too much, everything seems to work close enough, but if you want perfect transition to idle then its probably easiest to fit near the throttle body and vent to the usual place between the MAF and turbo. If you are using a cone filter it probably won't be much quieter.