I just saw an intake manifold off of a 328 e46 this weekend. Now I totally see why the hp is not any more than it is, and why the torque rating is so high. The intake manifold ports on the m52tu engined cars are noticably smaller than on the m54 cars. I am not really sure that intake manifold would be ideal for racing. I guess only time will tell.

Now for a street car, I bet an m54 manifold would be a nice upgrade for a 328.