The Suzuki GS series was Suzuki Motor Corporation's first full range of 4-stroke powered road motorcycles, having previously almost exclusively manufactured 2-stroke machines. Suzuki had produced the 4-stroke Colleda COX 125cc and 93cc 4-stroke single-cylinder machines in 1955 however the rest of Suzuki's production from 1952 to 1976 had been increasingly sophisticated two-stroke road machines, whose ultimate expression was the 750cc 3-cylinder water-cooled GT750. First models The first of the GS Series was the four-cylinder GS750 released alongside the GS400 parallel twin in November 1976. (1977 Model Year). The GS750 engine was essentially patterned off the Kawasaki Z1-900, and became the design basis for all air-cooled Suzuki four-stroke fours until the release of the air-oil cooled GSX-R. The GS750 engine was fitted into a dual cradle frame with telescopic forks, twin rear shocks and a front disc brake. The new GS750 was lauded for its handling at the time of its release, which was a significant improvement over its Japanese contemporaries, the older Honda CB750, the shaft-driven Yamaha XS750, and the more powerful but wayward handling Kawasaki 900. The GS400 was initially bored out to 423 cc (GS425), and subsequently enlarged to power the four-valve GS450, and with an eight-valve TSCC head used on the GSX400. The eight-valve design was later used on the GS500. The GS range was expanded in subsequent model years with a smaller 550cc four-cylinder GS550 and larger GS1000 added in 1977 with the range ultimately including 125cc single cylinder machines the GS125 and larger retro-styled machines such as the GS1200SS. Racing The good handling chassis and reliable, over-engineered engines made the four cylinder GS bikes ideal platforms for motorcycle road racing, with the GS1000 tuned by Pops Yoshimura winning the 1978 Daytona Superbike race, the 1978 Suzuka 8 Hours in Japan, and the AMA Superbike national championship in 1979 and 1980 with rider Wes Cooley. The bike won the Australian Castrol Six Hour race in 1979. In Europe, Yoshimura GS1000-powered Formula 1 bikes won the Formula TT World Championship ridden by Graeme Crosby in 1980 and 1981. Developments GS to GSX The original GS engine designs share common engine design elements of air-cooling, roller bearing crankshafts, two-valves per cylinder servicing a hemispherical combustion chambers with domed pistons and double overhead camshafts (DOHC) operating directly on shim and bucket tappets. In 1980 the first major upgrading of the 750cc and 1000cc machines with 16-valve (four valves