Originally Posted by Julesandtrish
FormerRotor, can you elaborate on how the secondary spring loaded section of the air filter box works? I see it, but don't understand how it works. Does it help blow off water/fluids that get in there?
Edited OP with pics for your reference J&T.
I'm obviously not a BMW design engineer, but it seems to me that the spring was likely selected to be compressed at a certain negative pressure to allow air into the box from the engine compartment. This would likely be useful if the intake were clogged so that the engine is not choked out.