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

Steady-state(I.e. highway driving) Fuel economy is heavily affected by internal friction. Even if the I4 and V8 are the same displacement the V8 will have more internal friction. It has 2x the cylinders, 2x the cams, 2x the rods, all of that causes extra friction, which means you need to burn more fuel to overcome the friction, which means you can’t have better overall fuel economy.