Wankel engines were invented in the early 1960s by Felix Wankel, a German engineer. Over the years, displacement has been increased and turbocharging has been added. Mazda rotary engines have a reputation for being relatively small and powerful at the expense of poor fuel efficiency. The engines became popular with kit car builders, hot rodders and in light aircraft because of their light weight, compact size, tuning potential and inherently high power-to-weight ratio—as is true for all Wankel-type engines. Mazda put the engine into series production with NSU (Ro80) and Citroën (GS Birotor) as part of the Comotor joint-venture between 1967 and 1977.