I remember learning in Classical Physics in college that the horsepower to drive a car on a flat surface was directly proportional to the drag of the vehicle as well as the cube of the speed.

Therefore, if it took say 30hp to drive a minivan down the interstate at 50mph to then triple the speed to 150mph would require (150mph/50mph) * * 3 times more horsepower or… 3 * * 3. 3 cubed is (3 * 3 * 3=)27 times more horsepower. 30 x 27 = 810hp. No stock minivan has 810 hp so no stock minivan can reach 150mph.

A Ferrari, however, might have half the drag of the minivan and would require only 15hp to drive down the interstate at 50mph. 15 x 27 = 405hp, so only 405hp would be required for the Ferrari to maintain 150mph, which many Ferraris can produce.

Much of the increased fuel efficiency came from the addition of electronic modules to control nearly every system in the automobile… engine control, fuel delivery, transmission control, power steering control, etc, etc, etc. Each of these advancements have added a few percent to the overall efficiency.

For example, power steering used to be accomplished by a hydraulic power steering pump on the serpentine belt on the engine. When you were driving on the freeway at 75mph, you were barely turning the steering wheel. Most of the power to drive the pump was unused and wasted. Electronic Power Steering (EPS) instead senses the need and then controls motors as required, providing roughly 3% overall fuel savings.

This same approach has been applied to every system within vehicles. Rather than add weight, electronics increase the fuel efficiency while reducing weight. For example, the EPS modules and motors weigh less than the hydraulic power steering pump, hoses and hydraulics that used to be driven by the serpentine belt.