Darin Cosgrove of Ecomodder.com decided to give his 1998 Pontiac Firefly a fuel economy boost by installing a custom “boat tail” mod on it. His car can now achieve 64mpg, effectively boosting fuel economy 15.1% at 56mpg over factory numbers. Video after the break. Click here for more pictures.

Cosgrove figures all of the mods cut the car’s drag coefficient from 0.34 to 0.23. That’s an unofficial, back-of-the-envelope figure he estimated using a pretty cool online calculator posted over at Ecomodder.com.

[via Wired]