[JackMcCornack]

> BSFC (IIRC) is based on WOT, and sea level, though.

I believe you indeed recall correctly, at least as far as available data goes. I've found it terribly hard to get BSFC info for anything other than full power at a given RPM. I'd expect BSFC to get worse as throttle (or fuel pump setting for us diesel folks) is reduced, since at low throttle there's still the same base internal engine friction to overcome as at high throttle (the extreme being whatever fuel is needed to idle--there's fuel going in but no power coming out) but how steep that curve is would be valuable to know.

It's been my experience that the rpm for optimum vehicle efficiency is lower than the rpm for optimum engine efficiency. In cruise, there's always more power available than is being used (otherwise we could never accelerate to cruise speed, plus we'd not have any excess available for when we needed it for hills or passing or whatever) and at some point there's a "sweet spot" where the less-efficient-due-to-low-revs curve crosses the less-efficient-due-to-low-throttle curve.

[edit PS--I turned 61 in June, but prefer to think of myself as 16 Celsius]