The 35mpg number is not only based on imperial gallons, it is also based on the Euro cycle for testing efficiency, which produces much higher numbers. An earlier poster commented that this engine will be more efficient than his 335d - um, no it won't. On the same euro cycle, the 335d is rated at 42.2 mpg combined, or 20% better. The same 335d is rated at 27mpg combined in the US, so using some math we can estimate that the 35mpg euro cycle figure for this new engine should translate to roughly 22.4 US mpg combined.
If it sounds like I'm ragging on this engine, it's because I kind of am. I just don't see the point of a gasoline 4 banger. It's not like it's anything radical or new. They could make a diesel 4 cylinder with the same horsepower and performance only it would get a very real US combined 35mpg. Now that would be an impressive engine. This? Meh.