http://gas2.org/2010/06/25/ford-mustang-v6-gets-48-5-mpg-around-bristol-race-track/2/
They achieved 48.5 miles per gallon. It reinforces my claim that slower speeds create better mileage, because energy is not needed to overcome aerodynamic drag. In addition, they only stopped to switch drivers very few times over seventeen hours. Acceleration of a heavy body uses up a considerable amount of energy. So, fewer changes in speed (that is, constant speed over a long period of time) will offset a heavier car, because constant speed means effect of the weight of the car is considerably reduced.
The energy efficiency of this particular v6 engine is particularly enhanced over typical engines in that the valve-timing is micro-adjusted many times per second. Instead of a V6 engine of several liters displacement, imagine that technology applied to the 125-cc engine that achieved this mileage:
http://gas2.org/2010/01/26/guy-mods-honda-motorbike-to-get-214-mpg/
...and this guy is not going around Bristol Motor Speedway. This is regular, real road mileage.
The weight of his vehicle is 231 pounds, 88 pounds heavier than the stock motorbike, so it again shows that weight is not as huge a factor as aerodynamics. And you cannot change the physics: as the Mustang test generously demonstrates, cutting your maximum speed increases any vehicle's efficiency. That is the "why" of 34 miles-per-hour. If the Mustang had traveled at a maximum of 34 miles per hour, I have no doubt that their mileage would have been in the 50-miles-per -gallon range (and the drivers bored tremendously going around an oval that slowly).
