better flame front propagation. Squish areas were also provided to the front and rear of the combustion chambers. The higher burn speed, coupled with lowered heat loss from the shallower combustion chambers created by comparatively narrow included valve angles and the flat topped piston meant that the GSX engines produced more power and torque than the same sized GS mills. The other major difference with the first GSX engines was the move from direct overhead cam actuation of the valve by shim and bucket of the GS engines, to valve actuation via short forked rocker arms in the GSX -the valves stems and springs being located inboard from the camshafts due to the reduced included angle between inlet and exhaust valves. Apart from the heads the GS/GSX engines were of a common design. The current range of bikes by that name are completely different designs that use derivatives of former super sports engines from the early-to-middle GSX-R series. Early GSX Among the earliest GSX models were the two-cylinder GSX 250 and the GSX 400. These Suzuki GSX models were the evolution of the GS series of two-valve-per-cylinder air and oil-cooled four-stroke motorcycles. The first four-valve engines were produced for the 1980 model year, but retained the "GS" designation for the US and Canadian markets until the release of the GSX-R models in 1986 (1985 outside the US). These GSX engines were based on Suzuki's "TSCC" (Twin-Swirl Combustion Chamber) engine design, and shared little with previous two-valve models. In 1999, only for the Asian market, the sport-touring Thunder GS 250 emerged. Subsequently, to be given the designation GSX in 2001. By 2005, that was then completely discontinued. The Suzuki Katana, which had the same "TSCC" engine design but, with the designation of GSX-S. Although, that had little in common with the more modern GSX-F Katanas which are, like the previously mentioned Thunder, sport-touring bikes. The TSCC engine was once again redesigned in 1983 with the introduction of a completely new GSX 750, Suzuki's first modern mono-shocked sportbike in both a naked (GSX 750E) and half-faired (GSX 750ES) version. Although this bike received solid reviews from testing magazines (and came to be the testers' preferred 750 sport machine for the year), its release was an ill-timed duel against Honda's all-new V4 engine in the form of the VF750 Interceptor. The 1983 GSX 750ES had air-adjustable anti-dive forks, preload and compression-adjustable rear mono-shock