One can only imagine if BMW engineers dreamed this up on a bar napkin or a chalk board. Under the hood is a 5.4 L M73 V12 from a E38 7-Series. BMW built the Z3 with 11 different engines, everything from a 118 horsepower 1.8 L M43B18 inline-four to the 315 horsepower 3.2 L S54B32 inline-six. With an engine bay able to handle so many different engines you can see why a lot of owners start dreaming of engine swaps.
Source: OppositeLock and Car & Driver