Calling the RX-8 the‘ final rotary-powered Mazda’ is only correct on a technicality. That’ s because Mazda has reinvented the Wankel engine for a different use. In the MX- 30 e-Skyactiv R-EV, Mazda has added an 830cc single-rotor petrol engine onto the SUV’ s electric motor to make it a hybrid vehicle. Unlike a conventional hybrid, however, when a car can drive using the electric or internal combustion engine, the MX-30 is always driven by the electric motor. Despite being positioned next to the electric motor, the rotary engine only acts as a range extender, a generator to top up the battery. The close proximity is so that the electric motor can be used to spin up the rotary motor; there is no permanent physical way for the internal combustion engine to drive the gearbox and wheels.
It seems a waste to use such an unusual engine, one so exotic and different, one synonymous with sports and racecars, as a measly generator. But there are numerous ways that a Wankel engine is actually perfectly suited for such a job.
The first is size. The rotor in the MX-30 hybrid is just 76mm wide – and with a single-rotor engine, that’ s practically the entire length of the engine. Despite its extremely compact size, it boasts an 830cc capacity with an output of 75hp. Mazda has also used aluminium side housings, sprayed with a ceramic coating, instead of the steel ones used in its previous Wankel engines to reduce weight.
Small and light engines make fewer vibrations, and rotary engines are already some of the smoothest internal combustion engines. Quite often, they are quieter too – when they’ ve not been tuned for high horsepower applications. So, as an engine to purr away as stealthily as possible, a rotary engine makes a lot of sense.
One of the downsides of a rotary engine is that you cannot employ variable valve timing to improve power or efficiency, as there are no valves. But a generator only needs to work at one rpm, so you can take advantage of its size, weight and smooth running and still make it incredibly efficient.
The two-rotor 13B engine powered Mazda’ s sports cars for decades
The RX-7 is the car many people most associate with Wankel rotary power
38 The Engine Rebuilder Issue 03