Mazda's Renesis rotary punches out 247bhp at 8500rpm, and 22.6kgm at 7500rpm.

Ask the managing director of Mazda’s R&D department, Phil Martens, what the benefits are of a rotary engine compared with a conventional reciprocating engine, and he replies simply: “You said it. The benefit is simply that it’s a rotary. It’s smoother, and there’s no way you can get that linearity of torque from a reciprocating engine.”

Though less powerful than the original 276bhp concept shown in the RX-Evolv two years ago, Mazda’s 1.3-litre Renesis rotary - destined for the RX-8 - punches out a healthy 247bhp at a lusty 8500rpm, and 22.6kgm of torque at 7500rpm. Otherwise, the production version sticks close to the concept. It has two rotors, each with three induction ports equipped with electronically controlled shutter valves to optimise the charge effect of the incoming mixture.

The Renesis also has twin drive-by-wire electronic throttles working in conjunction with the shutter valves, while a lightweight composite intake manifold smoothes intake gas flow.

The overlap between the opening of intake and exhaust ports no longer happens, making it possible to increase the inlet port area by 30 percent - a significant change over previous rotary engine designs. And whereas previous REs have a single exhaust port, the Renesis has two for each rotor, doubling the total exhaust port area.

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RX-8 will use new rotary engine.

he expansion stroke and overall efficiency has been increased as a result of the improved port designs. Unburnt hydrocarbons in the exhaust - one of the crucial legislated emissions along with CO (carbon monoxide) and NOx (nitrogen oxides) - are trapped in the exhaust chamber and fully combusted on the next cycle.

The bugbears of previous designs - poor rotor sealing, fuel thirst and port emissions - have been overcome in the new engine. “It’s naturally aspirated so we have been able to set the compression ratio to optimise the sealing of the rotors,” explains Martens. “The new port arrangement and twin spark-plugs help achieve cleaner combustion.”

The new engine doesn’t mean all Mazda cars will be rotary-powered; the company has revealed a new 2.3-litre, four-cylinder engine. “We’ll see conventional as well as unusual engines in the future,” says Martens.