Are you sure that ~4200 RPM isn't where the engine hits the REV limiter? If I used the REV limiter as redline, my own car would be most fuel efficient at 55%, which wouldn't make sense. But if we look at your car, 2400-6000 is exactly 40%. According to facts I've gathered from my research, THAT IS EXACTLY RIGHT!!! That is, I'm not surprised at all to hear your engine getting maximum fuel economy right at 40%, when it should achieve maximum fuel economy somewhere between 40% and 45%.
Another interesting thing you wrote . . .
According to you, your car gets its best mileage at 64MPH. Many people have posted that their car gets maximum fuel economy somewhere between 40 and 50MPH (and many of them are probably right, as their engine could be running close to optimum RPM at those speeds). Some have gone so far as to claim that such low speeds (regardless of engine RPM) should achieve maximum fuel economy in any car. They essentially say to slow down to save fuel. I'm sure that they would tell you that 64MPH is unnecessarily wasteful, because it is not fuel efficient. WHAT WOULD YOU SAY TO THOSE PEOPLE?
Me, I'd say that I'm not going to slow down to waste fuel just because someone else has their head up their butt. But I'd like to hear your view on the matter. -Dave
