wrong
Lower powered cars operating at closer to max power are more efficient than high powered cars operating at lower power levels. Stated another way...
a 100 horsepower engine operating at 100% output is more efficient than a 200 horsepower engine operating at 50% output. Both are generating 100 horsepower but the more powerful engine consumes more fuel.
I understand about pumping efficiencies, however cars typically cruise at about 10-15% of rated power with huge reserves ... if we were talking about 50% power and 100% power that’s one thing ,, what we have is a car using 6% power to cruise rather than 8% of it’s power ,, CARS ARE NOT AIRPLANES.
Every engine is different .. what you need to see is a chart/graph of BMEP vs. Fuel Burn to determine the engines most efficient RPM ... with a load equal to whatever “road horsepower” (rolling resistance plus aerodynamic drag) you need for a certain speed.. BMEP alone is useless on a dyno if you are just looking for max horsepower.