2011 Ford Mustang V6 rated 31 mpg highway

[Tmall]

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.

Because you have to rev it higher to get more power from the same displacement, and then they likely gear it lower so you're riding at a higher rpm for a given speed.

Just an example, car a is a 3.5 litre, car b is a 3.5 litre. One makes 200hp, the other 250. The higher hp one likely makes more power by spinning faster. It'll also likely have a shorter stroke and wider bore due to it's higher redline, to keep piston speed down. This will usually mean less low end tq, so they gear it so you're at 3500rpm at 60mph as opposed to 2500rpm for the lower powered car.

3500rpm time 3.5 litres gives you 12,250 litres of air/fuel being pumped through that engine. 2500 times 3.5 litres gives you 8750 litres of a/f mixture.

I hope that's what you were getting at slice, because that was a lot of typing that made my head hurt if not..