Cord wrote:
“Yes, max fuel efficiency is at lowest rpm with largest throttle opening.”
Yes, you are very right, but many people do not know this…
Rpm is directly related to fuel consumption simply because it represents number of ignitions (fuel burning occasions) within a given time.
Fully open throttle means engine needs less power to suck air in from the outside (less pumping loss).
Now, fully open throttle usually means high rpm. So, the best way to minimise gas consumption is to put a small displacement (power) gas engine in a car and let it drive with the throttle wide open most of the time. Honda did this with its Insight model. (Hybrid helped but real reason for its good mileage is its small I-3 engine, slippery body design and low rolling-resistance tyres.) This, however, leaves little reserve power for passing or going up hill.