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      07-08-2011, 01:14 PM   #9
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Drives: 2011 BMW 135i 6MT
Join Date: Jul 2010
Location: Canada

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The N55 engine has a cast iron crank, they are prone to break with too much boost.
"Prone to" would imply there are repeated examples of this happening. I haven't found anything on the forums in this regard. Not saying that we shouldn't be careful with pouring on the boost, but unless you have direct knowledge of failing N55 cranks due to high boost we can't say the N55 is crank "prone to" anything. At best it can be theorized that the crank may be vulnerable at high boost levels assuming it is indeed cast iron (which I also don't recall ever having been definitively proven). In any event, assuming none of the internals are forged I'd be concerned about the rods before the crank.