The Plymouth Duster I was a high-performance concept car of the Road Runner in the late 1960s. It featured the usual low curved racing type of windshield and had airplane-type flaps on the top and sides. There was a set adjustable spoilers on the side of the rear fender near the gas tank filler cap to prevent side-to-side yaw when slipstreaming in a race, with two more of them on top behind the driver, plus spoilers in the front rock shields to reduce frontal lift. It was powered by a 426 Hemi.

source: Wikipedia

A sure show stopper, the topless Road Runner concept car for 1969 was called Duster I, and came fitted with a 426-cubic inch Hemi-head engine that produced a whopping 425 horsepower. A built-in roll bar adjusted to match high-speed racing, and spoilers located in the rear quarter panels opened to prevent side-to-side yaw when slipstreaming. Smaller front rock shield spoilers helped to reduce frontal lift. Built on a shortened Road Runner platform, the wheelbase was reduced 16-inches to an even 100 inches, and the car rolled on large H60 x 15-inch tires.

source: www.chicagoautoshow.com