Turbocharged cars (exhaust driven) are more efficient partially because they capture waste heat from the combustion process. A manufacturer can tune the engine

Turbocharged cars (exhaust driven) are more efficient partially because they capture waste heat from the combustion process. A manufacturer can tune the engine and gearing to have a really good "sticker" EPA economy rating, but that generally doesn't translate to a good "actual" economy rating (because people are always gunning the engine to get that sweet boost). Unfortunately small turbo engines have higher emissions (forget the specific component, the other advancement of direct-injection has higher NOx emissions I believe) and manufacturers are now moving back to larger-displacement naturally aspirated engines because people don't drive like the EPA test works.