2009 BMW M3 Sedan: Tour de Airbox
September 14, 2009
This should help make up for last week's redundant airbox post. With the airbox lid removed we can see some impressive details which allow this monster to breathe. The bottom arrow points to one of the airbox's three intakes. This one supplies air which is gathered through the twin-kidney grille and routed above the radiator to this hole.
The top arrow addresses your questions about water draining into the airbox through the hood duct. The small slit in the bottom of the airbox offers drainage for small amounts of water. However, should some genius decide to run a garden hose in that duct, the overflow would simply drain out the intake hole in the front bumper (driver's side) which is the lowest point in the airbox. Click through for more details.
This view offers perspective from above and behind the filter with the camera facing forward and down into the airbox. The arrow in the foreground points to the same water drainage slit we saw pointed out by the top arrow in the above image.
The upper arrow in this image points to the daylight visible through the duct in the front bumper (see below).
BMW has done an elegant job of offering a huge amount of cool airflow to the engine without risking drowning the air filter and hydro-locking the engine. There's ample opportunity for air to get into the airbox and ample opportunity for water to escape.
And just to make it harder for you to mess with it, those crazy Germans attached the airbox lid with eight of these Torx fasteners
Josh Jacquot, Senior road test editor @ 8,671 miles