Originally Posted by vwrefugee
"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.
I have a friend who works at Alpina in Germany and they blew up plenty N55 engine all with crank failure. Cast iron cranks are glass hard and do not flex. The crank in the N54 is forged steel and has plenty of flex so it can deal with higher boost levels.