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

This was done in practice by WW2 pilots flying long range missions in certain aircraft. For instance, the F4 Corsair, normally with a 2800 cu.in. 18 cylinder radial engine. Dial the rpm way down, like 1800, and the boost up to maintain power. This was pretty hard on the engine, though.

Source: a close relative was a Corsair pilot for USMC.