It is here not about the V8. The principle is already history, and not a V8 in the M3 is more likely, probably be clear to everyone.
The only question is how the six-cylinder engine could be built ...
This time is an interesting statement from an engine developer of that manufacturer:
"So, watch out: BMW has always placed on the R6, because the smoothness was at the forefront as an engineer for engine technology, I can you but say the following. The biggest problem of R6 is that with ever-increasing power, the load block increase and crankshaft exorbitant. This is simply the length. biggest problem is the crankshaft. by their length, they must be condemned designed to be massively and so it is very difficult! and what is the greatest enemy of a sports engine? right weight! the heavier the crankshaft, the more sluggish revs up the engine! This might be for a silky AG-engine is a great feeling, but not for a sporty M-engine! Therefore, the F80, the crankshaft to about half of those of, for example 335i truncated and still housed six cylinders are! the engine is indeed a tad wider, but much shorter ... and winds up like hell!
And if you have not understood what I want now to say to you, then I can help you even more ... "