YES. And that is EXACTLY how my particular Otto Cycle internal combustion engine SHOULD perform. All cars are different obviously, but if they use an Otto Cycle internal combustion engine, maximum fuel economy will be achieved at close to 40% of the engine's redline. The only "difference" from one car to the next (buttuming they both use an Otto Cycle engine) will be what ground speed that most fuel-efficient RPM equates to. In many cars, that most fuel-efficient ground speed happens to be above 70MPH. My car is one of them. IF the engine RPM drops below 3000, the engine itself is less fuel-efficient. This means it takes more fuel to travel a certain distance, and COINCIDENTALLY, this means that it is less fuel-efficient at a lower ground speed. In your terms, this means that at 60MPH (for example), fuel efficiency is LOWER.
For an automobile to be most fuel-efficient at say, 50MPH, the Otto Cycle engine would need to be running near 40% of redline at 50MPH. IF that theoretical Otto Cycle engine was running at 40% of redline at a ground speed of 50MPH, then you would see a DECREASE in fuel economy at either 60MPH or 40MPH. Not because your ground speed changed up or down, but because the Otto Cycle engine was operating outside of it's most fuel-efficient RPM. (The ground speed change is coincidental)
I don't understand why you are questioning my test methods, when my results exactly agree with how Otto Cycle engines are supposed to work. If I said that I've found that water freezes at Zero Celsius, would you question how I measured that? Measuring MPG at certain speeds is so simple the average 2nd-grader could do the math accurately. Some of them could even do it in their head. I've performed the same measurements many times, with similar results. All of this was done before I even knew what results I should EXPECT to see. The fact is, my Otto Cycle engine should be most fuel-efficient at around 3200RPM. BEFORE I KNEW THAT, I'd noticed, through several years of driving experience, that the most fuel-efficient speed for the engine was 3500RPM. That means my particular Otto Cycle engine is performing EXACTLY as it should. If my tachometer is dead-on balls accurate, my Otto Cycle engine is most fuel efficient at about 40% of redline, EXACTLY AS IT SHOULD BE.
Yes, this means 78MPH is most fuel-efficient, and 70, 60 and 50 are less fuel-efficient. -Dave
