[redpoint5]

Originally Posted by wmjinman

OK, question # 2, then: How do I find my car's BSFC?

Good question, and I am not as knowledgeable as others on this subject. There is a thread on here that lists the BSFC of many engines, and similar engines will have roughly the same BSFC. The abbreviation is Brake Specific Fuel Consumption, and I believe it is a map that shows how much power is produced per unit of fuel throughout a range of RPM and throttle positions.

And I guess my test showed that 60 mph must have moved the engine's RPM out of the BSFC range? - and I guess 35 mph moved it out of that range on the other end?

More likely is that exceeding 60mph reduces efficiency due to aerodynamic drag.

You may be correct that dropping below 35mph put you in an inefficient engine operating speed. I would also believe moving this slowly up a hill is inefficient due to how much time is spent getting to the top.

One thing I did find interesting was that 40 mph, which I believe (from some basic testing) is my best MPG on "nearly level" ground is also "in the grouping" of best MPG speed on the hill (that paarticular hill, at least)

I also find this speed to be the most efficient on flat ground in top gear. It doesn't surprise me that it would also be an efficient speed when going up a hill because it's still fairly quick, but aero drag is relatively low.

And from what redpoint is saying (and quoting), maybe the reason it was just as good at 45, 50, and *maybe* 55 is because the BSFC (what is that, anyway - Best Specific Fuel Comsumption?) increases with speed at a rate that just offsets aerodynamic drag???? - but on level ground, with fighting gravity not being in the equation, the BSFC and wind resistance balance out at 40?

This sounds reasonable to me. Larger throttle openings are more efficient due to reduced pumping losses. Climbing hills requires more throttle opening, so it is relatively more efficient than the reduced throttle opening required to travel a flat road.