Stock-vs-stock, I know that, all other factors being a constant (ie car body weight, tire combo, etc.) a 4 cyl engine should theoretically consume less gas than an equivalent 6 or 8 cyl of the same aspiration.
Now I know souping up a 4 cyl to be as powerful as a larger engine is ultimately going to require more fuel. So my question is, if you soup up a 4 cyl engine, and a 6 cyl engine to the same horsepower level, will the 4 cyl still consume less gas? I realize the lighter weight would contribute to fuel efficiency, but I'm wondering if the engine itself is still consuming less fuel. I would imagine that for normal driving, the 4 cyl of the same horsepower would consume less since it wouldn't be at peak power production all the time.
Now let's say we have two engines with the same # of cylinders, but different displacement, both tuned to the same power level. I would ask the same question if the smaller displacement engine would still consume less gas.
Any thoughts, confirmations, or discussions would be appreciated.