Originally Posted by TheSt|G
N55 would certainly make it worse than the 1M, but the N54 is what they are using in the new M3. Certainly can't have the same engine in the cheap car.
Definitely put themselves in a hole here, but then again I've seen nothing definitive that a 2M is even coming out.
The new engine in the M3/M4 is the S55, as mentioned above.
Here's a discussion thread with a lot of info on the differences.