Darin Cosgrove, founder of Ecomodder.com, used just cardboard, aluminum and duct tape to make his DIY "boat tail", a mod that creates aerodynamic efficiency. The tail, attached to his 1998 Pontiac Firefly, extends the car by 4.5 feet and increases the fuel economy to 64 MPG.
"'I've driven with the tail on for about 300 km in total, mostly at highway speeds up to 100 km/h,' Cosgrove said. 'I didn't notice any change in handling. The only effect on driving is I have to watch out for rubberneckers in other cars. Seriously.'
The tail joins the rear wheel skirts, bellypan and other mods he's made to boost aerodynamic efficiency. The result isn't much to look at, but it boosted Cosgrove's fuel efficiency by 15.1 percent at 90 km/hr (56 mph).
By the way, 64 mpg is actually a walk in the park for Cosgrove, who used the 'pulse and glide' technique to get an astounding 99.7 mpg during the Green Grand Prix in May."
Video demonstration below.