Car & Driver tested a ringer(turbo) that did 13.4 or so in the 1/4! I don't think 13's are too much for an n/a (13.5-13.8, but no one's produced a timeslip to date. The M3 is mighty fast & weighs quite a bit more than an n/a!
There must be some one who with a knowledge of the M3's output curve tha will tune a modified (rebuilt?) n/a to do as well. I know that the n/a does not have the development of the M3, but with lighter weight & some tuning I'd like to believe a peak output could be produced @ the optimum engine speed to get that vaunted mid/low 13 time! 