I'm not sure they could have made it 20% more fuel efficient than the previous one with the use of a plain N54 engine. However, about 10% comes from the new transmission, but where does the other 10% come from ?
I'm not sure Alpina would go into so much trouble as to fit (and program into the ECU) a twin-turbo manifold on the N55 engine. The N55 is also not very well tested for this kind of power, while the N54 is tried and true.
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.
Last edited by kevinlevrone; 02-15-2013 at 07:04 AM.