No, I clarified the argument. I indicated that drag at 70 is only 1.6 times the drag at 55. At 110, the drag is 8 times as much as for 55 mph. These high performance engines are tuned for the higher speeds, and that is why they get poor milage at lower speeds. Air drag is not the controlling issue at lower speeds. Fuel economy WILL NOT increase as higher speeds are attained. Do you disagree with that? (Otherwise, you'd be able to get 60 miles per gallon at 200 mph.)
Mechanics allow me to have a car that gets better gas mileage at 70 or 90 than at 55.
Physics prohibits your claim at higher speed. No amount of mechanical ingenuity will defeat the increase in drag as the velocity increases. Ordinary friction does not increase with velocity. Air drag increases with the CUBE of velocity.
What do you suppose limits the speed of cars? The correct answer is "air drag". If you have a different answer, please enlighten us. Shape and profile rules change once you go supersonic, but the drag is still based on the cube of velocity.
You cannot win your case. This is just fact.
What case? Allow me to repeat: You flatly asserted that it was impossible (due to some nonsense about drag) for billbears' car to get better mileage at 70 than at 55. I indicated that my car gets substantially better gas mileage at 70 than it does at 55. No one was talking about higher speeds until you shifted context and threw up the straw-man. Your original assertion was demonstrably wrong. You can't make it right by claiming to have made some other argument.