I think the M42 is on the E30. The E36 4 cylinder are M43 or M44. I think I have an M43. Is there any way of finding out by looking at the engine. I am planning on installing the Downing Atlanta Supercharger on a fairly high milage engine. So I was thinking in the worst case if the engine blows why not put in a higher performing 4 cylinder. I would only do this if the new engine would fit exactly without any modifications (to the mount, transmission...). Of course the Supercharger still would have to fit.