Editing Wankel engine (section)

===Yamaha===
In 1972, [[Yamaha Motor Company|Yamaha]] introduced the RZ201 at the [[Tokyo Motor Show]], a prototype with a Wankel engine, weighing 220&nbsp;kg and producing {{convert|60|hp|abbr=on}} from a twin-rotor 660-cc engine (US patent N3964448). In 1972, Kawasaki presented its two-rotor Kawasaki X99 rotary engine prototype (US patents N 3848574 &3991722). Both Yamaha and Kawasaki claimed to have solved the problems of poor fuel economy, high exhaust emissions, and poor engine longevity in early Wankels, but neither prototype reached production.