2011 Ford Mustang V6 rated 31 mpg highway

[goof2]

Originally Posted by Homeslice

Well I'm not a physics major, but if you take 2 engines with the same displacement but different HP, I don't see how more horsepower ALWAYS means less fuel economy UNLESS someone is actually taking advantage of it by accelerating harder. And I doubt the EPA test is doing that, does it?

Personally I think the increased weight of today's vehicles is more to blame.

At its most basic more power from the same displacement requires more fuel and more air. When it gets more complex that trade off may no longer exist. One example is using aluminum for the block and heads vs. iron, better electronic controls, and requiring premium fuel allows a higher compression ratio in an engine before knocking occurs. That engine will create more power without increasing fuel requirements. It doesn't always mean anything, but it still stands as a good general guideline.

Increased weight is certainly a factor in lowering mileage, while increasingly more complex gearboxes help raise economy. There are a lot of things that will change mileage.