Intake tube kit / Direct intake kit for BMW 5 Series (F10/F11) with N55 engine code — TA Technix

A direct intake kit replaces the airbox with a short intake pipe and a conical filter. Two things change: airflow, because the airbox restrictions are removed, and the intake sound, which becomes clear and very noticeable under load - this is often the real reason for buying one.

All the performance gain depends on air temperature. A filter installed directly in the engine bay draws in air at 60 °C or more: it is less dense and gives back much of what it had gained. Proper kits come with a heat shield and a cold-air intake; without one or the other, the gain is theoretical. Carbon conducts significantly less heat than aluminium.