For an engine rpm yes, for a moving body, not so much. Energy in a vacuum is proportional to velocity squared, and energy required with wind drag is iirc 4th po

For an engine rpm yes, for a moving body, not so much. Energy in a vacuum is proportional to velocity squared, and energy required with wind drag is iirc 4th power of velocity. So even with an engine designed to be most efficient when the car drives 65 mph, the efficiency of the system will quickly be controlled by drag forces as speed increases.