Commonly referred to as an Air Flow Meter or HFM, this tube is a sensor that reads the amount of air entering the engine and indicates this amount to the ECU.
This HFM, with correct installation, is recommended for used on your BMW when making very high HP in forced induction applications.
This unit is 3.5" and increases the volume of air that the engine can take in, increasing horsepower... It will directly fit onto the Euro Air Box but will require an adaptor or European-spec intake kit to fit on the US spec cars (m50, m52, S50us, S52us).
This sensor has a greater reading range for airflow than even the euro or 540 HFM, making it perfect for your very high HP / boosted project.
Tech Notes:
The standard US E36 M3 intake tract is 3.0". If you're not using a specific 3.5" euro-sized intake kit, when you upgrade your E36 AFM to the 911 AFM (all 3.5") you will need This Sensor Adapter to fit the AFM to the intake boot.