If it has Valvetronic then it's an N55. My guess is that it does given the quoted efficiency numbers, but I would love to know for sure.
Quote:
Originally Posted by kevinlevrone
All BMW had to do to fix the N55 engine was to fit a Valvetronic head on an N54 and call it N55. Maybe that's what Alpina did...it would explain the fuel efficiency.
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That doesn't make sense though. It would make more sense to replace the N55 single turbo charger with a twin turbo setup (possibly adapted somehow from the N54, but possibly not). Changing an induction system is typically a lot less involved than creating a Frankenstein head/block combo, and no significant advantages lie in the N54 short block anyway.