Originally Posted by mkoesel
I appreciate what you are trying to say, but we mustn't forget that there are some amazing V6 engines out there as well. Consider the Nissan GTR, a car that competes in all performance categories with supercars costing up to ten times its price.
Speaking of supercars, and speaking of Jaguar too, credit must be given there as well: http://en.wikipedia.org/wiki/Jaguar_XJ220
It isn't necessarily the engine layout that will make the next M3/M4 a great car (nor any BMW for that matter, though it doesn't hurt either), but I agree with you that the I6 tends to have a better exhaust note.
I'm a car noob, but my understanding is the I6 is better balanced and more refined in terms of vibration, not sure about performance differences. The packaging is worse, hence why bmw puts the front axle so far forward relative to the engine. Audi on the other hand needs the B8 platform to satisfy everything from the RS5 4.2 to transverse mounted CVT A4's.
As a side note, I've read that Audi's current 3.0 engine is pretty outdated in terms of engine tech - specifically no variable valve timing. Seems Audi/VW has had problems with carbon buildup for the last decade or so, which could be due to egr use to reduce emissions. Seems like changing exhaust valve timing would be a better way to meet emission requirements and intake valve timing should improve performance.
Regarding your earlier post about RS5 availability, considering the B8.5 *just* went on sale here in the US, makes me think a new RS5 is still quite a ways off (3 years minimum). I haven't followed cars for very long, but Audi seems to have strange RS model availability, even more dubious in North American markets.