Originally Posted by Vreimann
Ok, so a guy I work with whom use to design components for BMW through a third party German company has a different answer about the purpose for this snorkel.
What he says is that at WOT and heavy use of the accelerator, the vacuum will allow the intake to open and pull hot air from around the turbo to help draw in cooler air to keep that area under the hood from getting too hot and to provide some general cooling.
Sorry, but that's just flat out wrong.
1. diesel engines have higher thermal efficiency compared to gas engines
2. has nothing to do with cooling
It is a dual stage intake, essentially there are 2 chambers to control the air velocity. I know it's hard to believe, but it is to improve torque at low RPM and help with higher RPM power as well, that's when that valve opens up and air is now being sucked in through that snorkel and into the secondary chamber, combining the 2 to make one big intake box.
Motorcycles incorporate intakes like this all the time and same goes for most race cars. The IS-F uses a dual stage intake box and I believe the NSX did as well.