[MeltMan]

Well, turbos are the most efficient way to add horsepower period. I dont feel that boosting should have any effect what so ever in MPG UNLESS, you are getting on the pedal. You see, when driving down the highway, you car is going to still be running the same A/F ratio as normal (unless modified), with or without boost to keep the same speed. With boost, you will have the throttle body open less than stock, letting less air in to maintain your speed. Until you get on the gas, then who gives a crap about MPG, you have a turbo.

Thats my take, other thoughts?

 

[MeltMan]

If you sprint a mile or walk a mile, isnt it going to take the same amount of energy??

No... Go sprint a mile and see how you feel. Then walk one and see how much better you feel. Keep in mind that gas burning in an engine is not the same efficiency through the whole rpm / mph range. If you floor it, you are not getting nearly as an efficient burn as if you ease into it. So sprinting a mile takes much more energy.