Originally Posted by 2m3
I agree completely with swamp2.
On S54: I heard many horror stories about the weak engine from my friends working at BMW service dept., plus no way a high rev M engine has an over bore configuration (long stroke engine???)
S54 has 91mm bore x 87mm stroke, so oversquare by a factor of 1.05:1. The S65 is 92 x 75.2, or a ratio of 1.22:1, so much more oversquare.