Why do larger engines get less MPG? Couldn’t a V8 be geared to a lower RPM and consume the same or less than an I4 at a given speed?

Question

I imagine some of the difference is due to weight (larger engines being in trucks) or performance (sports cars made to accelerate rather than cruise well), but it seems that almost without fail the bigger the engine the less MPG, I don’t understand where the extra energy goes if not to the wheels

In: Engineering

Answer 1

Between my vehicles the 6.2L v8 gets about 5mpg better than the 3.7L i5. I’m guessing aerodynamics and wheel/tire weight are the biggest factors here.