Quote:
Originally Posted by Ironring Racing
I think you misread my post, we're both agreeing a bore increase alone isn't likely.
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You're right I did misread it - sorrry (read "could" instead of "couldn't").
In any case, though, the fact is that reaching 3.5L with a bore increase alone isn't just unlikely, its actually impossible with the current N55 (or N54, or N53, or N52, etc) block. According to the displacement calculator I linked to earlier, the minimum bore size for a 3.5L I6 that uses the 89.6mm stroke of the current 3L N55 would be 90.4mm. Obviously you cannot bore a block with 90mm bore centers to 90.4mm.
Now, it's true that both bore and stroke could be increased instead. But as I already explained, even if they increase the bore to a 86.4mm - a size seen only in the iron block 3.2L S54 - a 98.1mm stroke is required to get to 3.5L. That's still way oversquare and a stroke that long is going to make operating at even the relatively low 7000 RPM redline of other modern BMW engines a dubious task indeed.
Simply put, there's a good reason why BMW has not increased the displacement of their modern I6 beyond 3L to date. It's because it is just not practical to do so.