The short-lived Plymouth Road Runner Superbird was a highly modified version of the Plymouth Road Runner with well-known graphics and horn. It was the factory's follow up stock car racing design for the 1970 season to the Dodge Charger Daytona of 1969, and incorporated many engineering changes and modifications (both minor and major) garnered from the Daytona's season in competition on the track.
The car's primary rival was the Ford Torino Talladega, which in itself was a direct response to the Mopar aero car. It has also been speculated one motivating factor in the production of the car was to lure Richard Petty back to Plymouth. Both of the Mopar aero cars famously featured a protruding, aerodynamic nosecone, a high-mounted rear wing and, in the case of the Superbird, a horn which mimicked the Road Runner cartoon character.
Superbirds equipped with the top of the line 426 cu in (7.0 L) Hemi engine with a pair of four barrel Carter AFB carburettors (2x4bbl) producing 425 hp (317 kW) could accelerate from 0 to 60 mph (97 km/h) in 5.5 seconds.
Developed specifically for NASCAR racing, the Superbird, a modified Road Runner, was Plymouth's follow-on design to the Charger Daytona fielded by sister company Dodge in the previous season. The Charger 500 version that began the 1969 season was the first American car to be designed aerodynamically using a wind tunnel and computer analysis, and later was modified into the Daytona version with nose and tail. The Superbird's smoothed-out body and nosecone were further refined from that of the Daytona, and the street version's retractable headlights (made of fiberglass) added nineteen inches to the Road Runner's original length. The rear wing was mounted on tall vertical struts that put it into less disturbed air thus increasing the efficiency of the downdraft that it placed upon the car's rear axle. For nearly 30 years the mathematic formula used to determine the exact height of the enormous wing was thought to be a highly guarded Chrysler secret. However, in the 1990s a retired Chrysler project engineer admitted publicly that the height was determined in much simpler fashion: it was designed to provide clearance for the trunklid to open freely. It should be noted that by a co-incidence the height of the wing was at the optimum level for maximum downforce. The rear-facing fender scoops were to hide cut outs. These cutouts were to allow wheel clearance due to the larger, wider wheels and lowered height of the vehicle for NASCAR. On Daytonas, the scoops were actually for ventilating trapped air from the wheel wells in order to reduce under fender air pressure and lift. For standard road going Superbirds the covers or "air extractors" were a cosmetic enhancement, for looks only. Ground clearance was 7.2 inches (18 centimetres).
Plymouth Roadrunner Superbird decal.
