Um then how do you explain this? From chevy's website their 4.3L V6 ecotech 4WD has 285 HP and 305 ft/lbs of torque. It has an EPA estimated 17mpg city and 22mpg city. So according to this, this engine get better or just as good mpg as my 2.7L I4 and more power.
So there is more power with same fuel economy. More get up and go did not decrease mpg. Im sure more examples could be found.
Fuelly.com is were I go to research gas mileage.