National agencies that tax automobiles according to displacement and regulatory bodies in automobile racing variously consider the Wankel engine to be equivalent to a four-stroke piston engine of up to two times the displacement of one chamber per rotor, though three lobes exist per rotor (because the rotor is completing only one-third rotation per one rotation of the output shaft, so only one power stroke occurs per working per output revolution, the other two lobes are simultaneously ejecting a spent charge and taking in a new one, rather than contributing to the power output of that revolution). Some racing series have banned the Wankel altogether, along with all other alternatives to the traditional reciprocating-piston, four-stroke design.