Originally Posted by Xelloss
Actually, almost all the M engines have been based on series production motors. The E46 M3's S54 was derived from the M54, E36 M3's S50 from M50, and the E30 S14 from the M10 block. Even the Mclaren F1's S70 was developed from the M70 block. The S85/S65 are the first to be truly bespoke and with BMW's desire to save costs, I believe they would like to return to that traditional formula as they have done with the S63/tu. With all the rumors flying about the V6, I have faith that BMW will stick to the glorious I6 for the E8X generation. It is just not financially prudent to allocate the resources to make a great V6 (not to mention the backlash from the BMW enthusiast community).
BMW also has a history of chopping two cylinders off the S85 and sticking in the E9x M3. That is where the V6 rumors come from, using the S63/tu.
Guess we will have to wait and see.