My thoughts are that its a vacuum reservoir, purpose is to provide vacuum to something under heavy acceleration when vacuum goes away. Should have 2 lines, one going to a vacuum supply and the other providing vacuum to something like brakes, HVAC, cruise control.
Thanks for you input! The pierburg you can see on one picture is a boost pressure valve 🤨 and the line feed to the engine as you can see on other pictures. Really cant explain whats that for lol… maybe someone who knows these engine could tell :/ are the any sites online with schemes etc? Iv been driving bmws for last couple of years and theyre gold when you need to find something online.