I also owned a 98 Z3 4 Cylinder, I went to Dinan for there performance upgrades, there CAI replaces the stock airbox and tubes up to the MAS. There cone filter runs down behind the fog lights but has a water proof cover that is washable to cover the filter. I also had a bored out throttle body and a stage 3 CPU download, this car could keep its own with the small 6 cylinder Z3's. The guy who bought the car from me hasn't had any problems with the CAI and uses the car as a daily driver.
:p