[azraelswrd]

I bet with some serious mods like adding a curved shield (optimized curvature) over the hood and windshield, grille blocks, wiper dam, front dam, side fairings for the wheels, removing the passenger side mirror, rounding out all the corners, belly pan, rear skirts, dumping the rear and passenger seats, yanking the radio/CD player/speakers/AC and attaching a boattail you will have dramatically better higher-speed mileage. It'll look something like the aerocivic... but taller.

But the aero should be better than the stock xB at the very least.