I was merely making a generalization about mileage. I.C.E.'s have way too many influencing factors to be exact about it.
But from a dynamics and physics standpoint, the only factors going into the energy required to move your car are weight and drag.
The only work your doing when you accelerate is to accelerate the mass (that includes overcoming inertia of rotating mass in the drivetrain). The only work your doing at constant speed is overcoming air drag. AND mechanical drag in the drivetrain, so obviously a big monster engine will need a monster tranny and rear, all things that have drag associated with them.
But that is IT!

Any difference is gas mileage between different engines in the same car are a result of mechanical drag, volumetric efficiency, and the driver.

If the mass is the constant, the same power put down to the ground will accelerate it at the same rate, whether or not that power comes from a 4 cylinder @ WOT, or a big block @ 20% throttle.

Same deal on the highway only the aerodynamics is the only factor (ignoring mechanical drag).


This is just a generalization, I'm not saying anybody's gonna get good mileage with a 540. It probably takes 100hp just to spin your drivetrain @ 6000rpm's.