I understand the 330i E90 (both US & European spec) has a variable, multi-stage air intake manifold (designed to give an improved, more even torque throughout range of engine speeds).

Likewise the 325i (but only in Europe, not the US 325i).

I believe there are a few different channels/paths for the air to flow through, and some actuators open/close the channels accoridng to engine rpm.

Think the old E46 had a two-stage intake, but believe the E90 has a three or four stage intake.

Can anybody shed any further light on how this all works?

And does anybody know at what enginre rpms's the multi-stage intake changes the air path on the 6-cylinder E90's?