No, I'm not butterting it. I'm simply repeating facts as stated by people who know a lot more about the Otto Cycle engine than either one of us do. There's a HUGE difference, there.
In some cases, YES, that's possible. I haven't experienced it myself, but have no reason to doubt that it could happen. For my current car, the most fuel-efficient speed is 3500RPM, 43% of redline, and 78MPH (take your pick, all are correct). Several cars I've owned have been most efficient somewhere above 70MPH. To think that a car MIGHT be most fuel-efficient above 90MPH is not too hard to imagine. That's only about a 13MPH difference from my own car, and it's not exactly a sports car.
Most automotive authorities
Yes, but do those "automotive authorities" realize that at optimum RPM of an Otto Cycle engine, less energy is wasted as heat, leaving MORE ENERGY available to keep the car moving? Again, it's not really that you are pulling extra energy out of the engine, it's just that the engine is converting more of the available energy to kinetic energy. Thus, the greater fuel efficiency.
ON THE OTHER HAND, it's easy to believe that many cars would indeed be more fuel efficient at 50MPH than 90MPH, because (NOT coincidentally) some Otto Cycle engines are running closer to 40% or so at 50MPH than 90MPH.
But a blanket statement like slow down to save fuel isn't necessarily going to be helpful for all circumstances, unless slowing down brings your Otto Cycle engine closer to the 40-45% range where it is most uel-efficient. -Dave
