1983 320i here
I added a K&N free flow filter, removed the big ugly air box, nice growl now.
replaced coil with a MSD coil, added 10Kv worth of spark, picked up the milage by about 2km/ltr. Bosch Platinum 4 plugs. PIAA driving lights, 205R13 BFGs, Air/gas shocks, and a Kenwood sound system. Just got to work on the body now.
Plan to add a better header and exhaust system, tighten up the steering a bit and play around under hood some more.
I may even rebuild a block from the ground up, Love the 320, what a great handling little lady but need to get the rear end to stick a little better, it can slide a bit on wet pavement.
You can get some great deals from you local BWM wrecker yard. Anyone looking for parts in western canada or Northwest USA try Tomcat Auto in victoria, BC