[rwhyde]

Sorry, I am late to this party/question. Stepping back to the original question of identical engines, one with turbo and one without, which gets the best mileage (also assuming same gearing), the answer to me lies in which one puts the LEAST amount of air in the cylinders, thus requiring less fuel. If your turbo puts more sir in the cylinder, then more fuel is required to attain a perfect A/F ratio. This is why manufacturers are moving to smaller displacement along with the turbos to get as much if not more power and then equal or better economy. Of course some direct injection and such help as well. When you can reliably get 400hp from 2 liters, then who needs mega displacement. But i digress, back to fuel economy. Certainly upping compression, along with direct injection to avoid detonation and variable cam timing, all are key elements in optimizing fuel economy and still offering performance when required to keep things fun. One of my earliest mentors told me that the best fuel economy was attained at the peak torque (not hp) of any engine. OF course that was long before variable valve-timing was in everything.