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Even if the sealing is absolutely right, the basic principle of the rotary creates some difficulties. Whereas a single cylinder breathes in petrol and only later puffs out exhausts gases, a single rotor is constantly doing both, which means high fuel consumption and an awful lot of emissions.

A lot of noise, too, if you're not careful. The Mazda RENESIS unit is well muffled, but sporting rotaries can make quite a racket, and some of them are ear-splitting. The reason is that, as with two-stroke engines, one of the best ways of tuning a rotary is to fit a megaphone exhaust. This doesn't just fail to reduce engine noise, it actually magnifies it, with spectaular results. The beautiful little 1960s single-rotor NSU Spyder racer (pictured above), which was demonstrated at Donington a couple of years ago, belied its appearance by being shatteringly loud, while the Mazda RX-7s which dominated the British Touring Car Championship in the late 1970s were even worse.

Since the rotary has a competition history (which includes Mazda winning the Le Mans 24 Hour race in the 787B sports car pictured below) it's clear that the engine can produce a lot of power. But it does this because it revs so easily. As explained in our feature, an engine's power equals its torque multiplied by its speed. Rotaries spin very quickly, but they don't produce much torque. The explosion of the fuel/air mixture skims along the top of the rotor rather than pushing heavily on to a piston. If the piston engine's operation is like the action of a cyclists' legs, the rotary does the equivalent of pushing the tyres with the flat of your hand.

Rotary engines are in this respect the exact opposite of turbo diesels. Their ability to rev isn't merely useful - it's vital if they are to produce decent amounts of power. The Mazda RX-8 has decent mid-range performance, but that's despite the basic characteristics of the rotary rather than because of them. Even then, the RX-8 really needs to be taken beyond 6000rpm before it starts to perform properly.

I can't have been more than about ten years old when I first learned about Felix Wankel and his rotary engines, and I've been fascinated by them ever since. I'm delighted that Mazda has kept the faith and brought the rotary into the 21st Century with the RX-8. But even I have to admit that the rotary's place in the car industry is that of a low-volume novelty. For all its faults and crudeness, the piston engine is still the boss, and justifiably so.

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