Turbo charging off topic

If you build two IDENTICAL engines...meaning mechanically...the turbo car will get worse mileage if the components related to the turbocharging are the only differences.

Supporting concepts:
Pre-boost, you have less efficient movement of exhaust gasses because of the turbo being, essentially, an obstruction in the exhaust system.
Post-boost, just as stated - when the turbo charger increases the amount of intake air, the fuel must also be increased. You get more power, but it takes more gas to produce it.

Having said all that - what makes turbo cars so efficient is that the engines are NOT identical (mechanically) to their normally aspirated counterparts.

Now, if you had said something like, "two engines that produce the same identical peak horsepower but one is NA and one is turbo'd"...then you could handily argue that the turbo engine would be the more efficient because it would, rationally thinking, not be producing boost all of the time, could be of lower displacement, and would be engineered to mitigate some of the negatives associated with turbocharging. In short, it might take 3 litres of NA engine to match the output of a 2 litre turbo motor and, during most of your low-power cruising or coasting, the 2.0 would be naturally using less petrol.

See, that was easy!