Originally Posted by swamp2
Let's look at piston speeds. US units, sorry Uli...
N55: 68.6 ft/s
S65: 69.1 ft/s
S63Tu: 70.1 ft/s
Thus non-stroked S55(?) at 7500 rpm: 73.5 ft/s
Stroked S55(?) to 3.2l at 7500 rpm: 78.4 ft/s
Ferrari 458: 79.7 ft/s
I know, I know don't compare BMW and Ferrari. That complaint falls flat though when looking at the S65, it is the closest to a Ferrari engine in any other production car.
From this I think it is fair to say that even a stroked 3.2l S55(?) could support a redline of 7500 rpm.
Of course there is the question of Valvetronic and its rpm limit. I've only heard rumors about that.
I never said that its impossible, but high piston speeds in combination with high pressure turbos make problems were all this force come together ... at the crankshaft and its bearings ... and an longer crankshaft is in this case much more problematic than an shorter one ... remember the problems of the S54 with this parts. Also tortuosity could become an problem at an longstroke high-pressure turbo inline-6. with its long crankshaft.
Its expensive to reinforce the chrankshaft and the bearings so that they could withstand this forces ... esp. in longer times in use ... and I donīt know if BMW would do this, if cost-reduction is the main issue and they are of the opinion that 420hp are enough to be better as all competitors.