The roots of the GPz550 (GPzs would be seen in 550, 750, 1100, and 305 iterations during the early and mid-1980s) can be traced primarily to the mighty 903cc Z1 of 1973 and the machines spun from it. As the Z1 developed during the middle-to-late 1970s, becoming the KZ900, KZ1000 and the café-flavored Z1R of 1978 (which would strongly influence GPz styling), Kawasaki also began building smaller fours with the same performance focus. These were UJMs, for sure, but very good ones. The rapid, 750-beating KZ650 of 1976 came first, followed by the highly capable KZ550 of 1980 (upon which the first GPz550 was based). The KZ550 was basically a 3mm overbore version of the Euro-spec Z500, introduced in 1978. A 400cc version, the Z400, was also produced for the Japanese market in ’78.