I was looking though SAE paper 780633 again, and noticed that I missed the actual BSFC map they published. The graph that I included in my previous post only works for full load. But the graph in this current post is the complete map of BSFC as a function of RPM. So you can use this map to predict fuel consumption changed from gearing changes. Hopefully at least one person out there finds looking at this info interesting.

As an aside, they also include "Road Load" for the 300sd (the focus vehicle of this paper). This is basically how much power is needed to go a certain speed. It is the exact same thing I tried to predict for my 220d in my first post. Unfortunately, they don't explain how that curve was calculated. There are a lot of assumptions that go into that calculation, so it would have been nice if they had documented their assumptions. Or, I guess there is a chance that MB provided that info. It really isn't clear how this graph was created.

Not sure about people's onroad experiences, but this paper suggests that for a given vehicle speed, the turbo version of this engine is actually more fuel efficient than the NA version (and the 240D as well). That is impressive engineering, in my opinion. See 2nd graph attached to this post.

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