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My first thought would be fuel. Maybe the first one was lean this one is rich. It may run fine, but until you get a Wideband O2 or something similar to check the a/f ratio you wan't know for sure. Of course theres a lot of differences between engines and how efficient they are at converting combustion into useable power, including head flow, spark plug gap, exhaust flow characteristics, etc....
That being said don't compare numbers between other cars as a goal. If you're confident that the car is tuned up and running correctly you have to learn what driving method can get you the best mileage.
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