There is no need of CAI for our engine. Even the stock filter is plenty. With all the diesel tunes out there the boost pressure increase is very conservative, some even don't increase it at all. If you really looking to increase the performance of your motor, install a tune and an IC or meth from BMS when released in the future. Exhaust or CAI on NA diesel is not worth your lost warranty since there is really no exhaust to begin with, it ends right after turbo. Even there most of the gases has been already recycled by the 2 EGR valves. Everything past turbo is a very complex regenerating system that produces a steam of H2O, that's why there is no black residue on your tailpipes.
Retired: 2005 N52 E90 330i Sport 6AT
Retired: 2007 N54 E92 335i Sport 6AT
Current: 2012 M57 E70 X5 xDrive35D