Yeah, I agree, but In-line six 4 strokes are perfectly balanced naturally and so are V12s for the same reason (2 IL 6s). It may be that the high revs necessary to get 650 out of a 5.5 liter required a 12 to keep it together considering the high compression of a diesel . . . My first guess. Beeee-u-tiful though ain't it?5.5L is a tad small for a V12 I would think.
Although it does produce 650 HP.
Racing engine for Audi.