The performance car market segment expanded during the late 1960s and early 1970s. The 1964 Barracuda fastback is considered the first of Plymouth's sporty cars. Based on the Valiant, it was available with the Slant Six, or small block V8. For 1967, Plymouth introduced the Belvedere GTX, a bucket-seat high-style hardtop coupe and convertible that could be ordered with either the "Super Commando" or Hemi V8 engines. Looking for an advantage at the drag races, 1968 had a stripped-down Belvedere coupe, the Road Runner, which featured a bench seat and minimal interior and exterior trim, but was available with Chrysler's big-block engines and a floor-mounted four-speed manual transmission. The Barracuda, originally a "compact sporty car", became available with the 426 Hemi and 440 big-block engines in 1968. The GTX, Barracuda, Road Runner, Sport Fury GT, and Valiant Duster 340, were marketed by Plymouth as the 'Rapid Transit System', which was similar to Dodge's 'Scat Pack' concept. During this time, the brand also competed in professional automobile racing. Examples include Richard Petty's career with Plymouth in NASCAR; Dan Gurney, who raced a 'Cuda as part of the All American Racers in numerous Trans Am events; and Sox and Martin, one of the most well-known drag-racing teams of the period, only raced Plymouths after 1964.