Quote Originally Posted by blacksambo View Post
As far as power and mpg is concerned, with normally aspirated engines, there is no way on earth with more hp you can get more mpg, all things being equal. It's against the laws of physics
Read up on these so-called law of physics. Many engine builders know that a more powerful engine is a more efficient one. By that, I mean more of the air/fuel mixture goes to making power and moving the vehicle.

There is a measure of efficiency (called volumetric efficiency -- VE) that is a measure of cylinder filling. (There is also a percentage loss of power thru the drivetrain -- which is unimportant and a constant for this discussion). Better VE means more power. And, it means better leverage to propel the car. The problem with more power is people mostly use it go accelerate faster and to "hotrod". The problem with your generalization is a more efficient motor can pull the vehicle with less "effort". If you succeed in making an engine more efficient, driving it the same will result in better MPG.

Newer E10 fuels make cars look worse though. And, they are. Alcohol fuels have less BTUs compared to gasoline. So, the dilution of gasoline with corn-fuels lower the BTU rating -- and it's power. It takes more E10 fuel to get the same amount of power as pure gasoline. So, engine efficiency is going down -- without even trying.

If, somehow, you can create a better burn and more heat, you will make more power. As such, you will make better use of the fuel you burn -- which ends up with a more efficient vehicle.

Whether you use that extra power for better MPG or more fun is up to you.