Not advocating being stupid in the car...please drive responsibly. This is more a question of, by going easy on the pedal and just driving smarter, can you squeeze that extra mile or two outta a gallon of gas?
in a 4 cylinder YES, in a v6 yes, in a high geared v8 yes
in a low geared v8 like my dads old 69 ford 1 ton, it didnt matter if it was driven easy with no load or driven hard with 20k on a trailer it got 6 mpg
our suburban? driven easy gets 18mpg, drive it hard and it drops to 10
