The highs & lows of the rotary engine

But this isn’t the only option. Some manufacturers have used, or at least experimented with, rotary engines, which at first sight appear to have a much more clever design. The fact that they have not become universal, despite having been available to the public for nearly 60 years, shows that this isn’t entirely the case.

Nevertheless, they are fascinating devices, and well worth a look. We’ll start with a brief investigation of their history and design, and then discuss 36 actual or planned rotary-engined cars, in approximate order (because the timescale isn’t always obvious) of when they appeared:

More than one type of engine can be described as a rotary. We’re looking here at the Wankel type, named after German engineer Felix Wankel (1902-1988).

No rotary engine fitted to a car has ever exactly followed his original idea, but they are named after him because he came up with the concept of one or more rotors which surround, and drive, a central crankshaft, from which power is taken through the transmission to the driven wheels.

As the Wankel engine is understood today, it consists of a more or less triangular rotor (or rotors) spinning eccentrically in a chamber which is roughly the shape of the number eight. For every spin of the rotor, the usual process of taking in a fuel/air mixture, compressing it, igniting it and expelling the resultant exhaust gases happens three times. The crankshaft turns three times during this process, since it’s geared to the rotor at a ratio of 3:1.

Rotaries have a reputation for achieving high revs, but this is slightly misleading. When the engine is said to rev at 9000rpm, the crankshaft turns at that speed, and there are as many combustion cycles as there would be in a piston engine operating at that rate, but the rotors themselves are turning at only 3000rpm.

Wankel rotaries operate very smoothly, partly because each combustion event is relatively small, and partly because the rotors are always in motion. There is no equivalent of a piston starting at rest at the top or the cylinder, accelerating and then decelerating on its way to the bottom, and repeating that process on the way back up. This is a matter of greater concern in a piston engine than most of us realise, but it isn’t an issue at all in a rotary.

Rotaries are also very much shorter than piston engines. If, say, they are mounted in the front, their mass is therefore concentrated closer to the centre of the car. This is excellent news in terms of weight distribution, and helps to explain why rotary cars often handle exceptionally well.

It’s in the nature of a rotary engine that it takes in fuel and emits exhaust almost constantly. This is often bad for economy and emissions, which is one of the main reasons why this type of engine has never really taken off, despite its advantages. Rotaries are also not known for their torque. The rotors are always spinning, and there is nothing to compare with the force of a combustion event pushing a piston directly down a cylinder. 

When rotaries produce a lot of power, it’s because of their high revs, not because of their torque. Yet another problem, which has caused some manufacturers to abandon rotaries before putting them into production, is the fact that the tips of the rotors have to create a perfect seal with the inside of the chamber without damaging it. Any failure is disastrous, and usually leads to the engine having to be scrapped.

NSU, now buried somewhere within the Volkswagen Group, was the first manufacturer to take the Wankel rotary engine seriously. It had a prototype running in 1957, and seven years later put a later development into a production car.

This was the beautiful little Spider, which was derived from the Prinz saloon. It had a rear-mounted single-rotor engine, and was quite successful in competition, where – if fitted with a megaphone-type exhaust which suits rotaries very well – it was staggeringly noisy.

The first of many rear-engined Skodas was introduced in 1964, the same year as the NSU Spider, but it occupies a very different place in the history of rotary engines. That’s because no production model was ever fitted with one. A few rotary prototypes were built, but Skoda decided to stick with pistons for the cars it sold to the public.

This seems to have been the first time a manufacturer cancelled a rotary project before production began, but it definitely wasn’t the last. Within a decade, the same thing would have become almost commonplace

In 1965, Curtiss-Wright (best known previously for its aeronautical work) bought an early example of the recently-introduced first-generation Mustang, removed the 4.7-litre Windsor V8 engine and fitted its own RC2-60 twin-rotor.

Curtiss-Wright hoped that the project would lead to it becoming a supplier of rotaries to the US auto industry. The car attracted a lot of interest, but manufacturers turned down the opportunity. Contrary to Curtiss-Wright’s dreams, the car, which now lives in the National Auto & Truck Museum in Auburn, Indiana, is believed to be the only rotary-powered Mustang ever built.

PICTURE: representative 1965 Mustang

No other manufacturer has committed itself as intensely to rotary engines as Mazda, which you will therefore be reading a lot about here. Its first rotary car (and indeed its first sports model) was displayed at the 1964 Tokyo Motor Show, but the twin-rotor was proving difficult to manage. It was only after Mazda developed new seals that the rotors stopped creating gouges in the casing, known to the exasperated engineers as “the devil’s claw marks”.

Much more powerful than the NSU Spider, the Cosmo Sport finally went on sale in May 1967. A 1968 update included several improvements, including even more power, and the car remained in production until 1972.

A few months after the Cosmo Sport entered the market, NSU became the first manufacturer to produce a second rotary model. The Ro 80 would have been remarkable even with a conventional engine – its looks, its aerodynamic efficiency, its all-round disc brakes and independent suspension, and a clutch operated by touching the gearlever were all well out of the ordinary for a mainstream car introduced in 1967.

Its rotary engine was a highlight too, at first, but the global oil crisis of 1973 and an increasing awareness of harmful exhaust emissions badly weakened its case. Miserable unreliability in the early days didn’t help either. That issue was soon fixed, but the Ro 80’s reputation never recovered. Although it survived for a decade, it was the last NSU model ever sold – a unique case of a brand being brought to its knees by the rotary engine; NSU was acquired by Volkswagen for a song.

Since the Cosmo Sport was never going to sell in large numbers, Mazda realised that if it was to make any headway with the rotary engine it would have to fit it to more conventional models. This process began in 1968, when the company added a rotary to the second-generation Familia saloon, which had been introduced with piston engines the year before.

The car was never well known outside Japan, but the related R100 (as the Familia Rotary Coupe was known in export markets) was far more famous, partly because it was the first Mazda exported to the US, starting in June 1970.

PICTURE: Mazda R100

Luce was the name of several cars produced from 1966 to 1991 with both piston and rotary engines. The R130, launched in 1969, was an outlier in the range.

Not only did it have a beautiful coupe body designed by Bertone, it was also, and remains, the only Mazda with a rotary engine directly driving the front wheels, a layout not used for any other Luce no matter what engine it had.

Derived from the Ami, but wearing a dramatic fastback body produced by Heuliez, the M35 was powered by a single-rotor engine produced by Comotor, an ultimately disastrous joint venture between Citroën and NSU. No M35 was ever sold to the public, but from 1969 to 1971 a few hundred were given to existing Citroën customers, who evaluated them in plain sight – there was even a sticker on the rear window which explained to interested passers-by what was going on.

After testing, the cars were returned to Citroën, but many of them have ventured into the wild and are now in private hands.

The series of C 111 experimental sports cars, which first appeared in 1969, were mostly powered by rotary engines, initially a 280bhp three-rotor and later a 350bhp quad-rotor. Mercedes later switched to conventional piston engines, and now says that this was because of reliability and durability problems.

However, Wolfgang Kalbhenn, now retired but a Daimler engineer for over 30 years, has written that rotary development continued until 1975, with the intention of fitting engines of this type into saloon cars. Nothing came of that, and the C 111 remains the only rotary Mercedes ever seen in public.

Mazda’s RX naming convention, applied to rotary-engined cars sold outside Japan, began in 1970. The RX-2 was known on its home market as the Capella Rotary, the Capella being a mid-sized saloon or coupe larger than the Familia but smaller than the Luce.

Mazda had by now firmly established itself as the most prolific manufacturer of rotaries. Production reached 100,000 in the year the RX-2 was launched. By contrast, NSU, the pioneer in the field, built fewer than 40,000 vehicles of this type from 1964 to 1978.

Along with the Nissan 126x and the Toyota EX-7, the RX-500 was one of three exceptionally daring Japanese concept cars revealed in 1970. Despite its fashionable wedge shape, butterfly doors and gullwing engine covers, it was promoted largely as a safety test-bed, and had (like the Nissan) tail lights which indicated to following drivers whether it was accelerating, slowing down or maintaining a constant speed.

It was almost unimaginable that either Nissan or Toyota would have fitted rotary engines to their concepts (in fact they had a 3.0-litre V6 and a 5.0-litre V8 respectively), and almost equally unimaginable that Mazda wouldn’t. The twin-rotor unit mounted just ahead of the RX-500’s front axle had a quoted output of around 250bhp.

Despite having a larger number in its name, the RX-3 of 1971 was smaller than the RX-2 introduced the previous year. In Japan it was known as the Savanna, which was Mazda’s name for the rotary version of the Grand Familia, sold in export markets as the 818. The Sports Wagon, launched in 1972, was the world’s first rotary-engined estate car.

On the market for seven years, and in three series, the RX-3 was a sales triumph. 286,757 were sold in that period, 105,819 of them (more, you’ll remember, than Mazda’s total rotary production up to 1970) in its peak year of 1973 alone. This made it the best-selling rotary car ever produced up to that time, and it is still second on that list today.

The RX-4 was the export rotary version (an idea you’ll be familiar with by now) of the second-generation Luce, and was the direct replacement of the earlier Luce R130.

The largest RX model yet was introduced in 1972, and was available as a saloon, a coupe and, later, an estate. Annual sales never quite reached 100,000, but the RX-4 outsold the smaller RX-3 every year from 1974 onwards.

Nissan took the rotary engine very seriously in the 1960s and early 1970s, and got as far as displaying a prototype twin-rotor Sunny (the Japanese name for the car sold elsewhere as the Datsun 1200) at the 1972 Tokyo Show, with suggestions that a production version would follow.

However, there was no equivalent model at the same event in 1973, the implied production car was never released, and during 1974 Nissan announced that it would be taking the matter no further.

The car now known as Aerovette was given that name after it was fitted with a 6.6-litre Chevrolet smallblock V8 engine. Its original power source was part of GM’s rotary engine programme, which you’ll be reading more about shortly.

The programme was based on a twin-rotor which, when the concept was first shown in 1973, seemed likely to go into production. The concept had a quad-rotor, which was essentially two of the twin-rotors joined together.

Alfa Romeo ran its own rotary programme, and got as far as putting experimental engines of this type into a Spider sports car and a 1750 saloon.

While other manufacturers retained their enthusiasm for rotaries beyond 1973, Alfa Romeo decided in that year that it wasn’t worth pursuing, on the grounds of poor reliability and high fuel consumption. The only remaining solid evidence of the project is a surviving engine, which is now stored at the Alfa Romeo Museum in Arese.

The General Motors rotary engine programme started in 1970, the same year the Vega went into production. There was obviously no possibility of a rotary Vega at that time, but such a vehicle was at one stage being talked about for the 1974 model year.

Prototypes were built and tested, but the production rotary Vega became one of the many casualties of GM’s decision to walk away from Felix Wankel’s idea. Around two million Vegas were sold from 1970 to 1977, and every one of them had a piston engine.

Emboldened by the positive reaction to the M35, Citroën put another Comotor engine (this time with two rotors rather than just one) in the brilliant GS in 1973. Quite apart from the fact that it was vastly more expensive than any other GS, the Birotor guzzled fuel at a phenomenal rate, which was exactly the sort of thing nobody wanted at the start of a global oil crisis.

Sales were, naturally, pitiful, and the whole project collapsed almost immediately. Citroën used a development of the same engine in – and if you didn’t already know this you certainly won’t be expecting it – a helicopter. In 1974, the company collapsed and had to be rescued by Peugeot. The GS Birotor wasn’t the sole cause of this, but it didn’t help.

Unlike the earlier Vega, the Chevy Monza was intended to be available right from its 1975 model year launch with GM’s twin-rotor engine.

An attentive reader such as yourself will need no reminding that the abandonment of the rotary programme made this impossible. Vegas were sold with engines containing four, six or eight cylinders, but no rotors.

The second-generation B-Series had already been in production for nearly a decade when Mazda decided to fit it with its by now very common Wankel engine, thereby creating what is believed to be the world’s only rotary pickup truck.

It was sold only in the US and Canada, and you could buy a new one from 1974 to 1977. If you needed evidence of how the global oil crisis affected enthusiasm for rotary-engined vehicles, you’ll find it in the fact that of the approximately 15,000 Rotary Pickups ever made, nearly all were built in 1974.

If early plans had come to anything, American Motors Corporation would have offered a rotary engine in the Pacer (possibly with front-wheel drive) from its introduction in 1975. The problem was that the engine was the one developed by General Motors, and by 1975 GM wasn’t even building it, let alone supplying it to anyone.

Instead, the Pacer went into production with AMC’s trusty straight-six engine, and later with a 5.0-litre V8, both driving the rear wheels.

Perhaps the most obscure of all the Mazda rotary cars had a name which shimmered with irony. The 1975 Roadpacer was heavy for its power output, and therefore didn’t pace along the roads very quickly, while AP stood for Anti Pollution – not a characteristic for which rotaries are normally renowned.

In a further twist, the car was actually a Holden Premier, built in Australia and shipped to Japan without its usual engine so that Mazda could slot in its own twin-rotor unit. This made it the only GM-built rotary car to enter production (admittedly in very small numbers), even though it wasn’t part of that company’s rotary engine programme.

Known as the Cosmo in Japan (though completely different from the original Cosmo Sport), the RX-5 was introduced in 1975, a few months after the Roadpacer AP. It was the smaller of the two cars by several inches in every direction, but at the same time it was the largest of all the RX models sold in the 20th century, to the detriment of its straightline performance.

Although reasonably successful, the RX-5 did not attract anything like the same attention as the RX-3 or RX-4, and has been largely overshadowed by the next model in the series, which became the most popular of all the Mazda rotaries.

Lada Classic is both the title of a 1980s snooker tournament and the collective name for a long series of Fiat 124-derived saloons and estates built in Russia by AvtoVaz.

Of the several million produced, nearly all had a four-cylinder petrol engine with a capacity of between 1.2 and 1.5 litres. The very few exceptions were fitted with single- (from 1978) or twin-rotor (from 1983) units, and were mostly sold to authorities rather than the general public. Reliability is said to have been problematic.

Over three generations from 1978 to 2002, Mazda built 811,634 RX-7s, a productivity rate which no other manufacturer of rotary-engined cars has even approached. The first-generation car accounts for more than half the total sales, and is therefore the most popular standalone rotary model.

Its success was no doubt helped by its very visible success in top-line motor racing. RX-7s won the 24-hour events at Spa and Daytona, the Australian Touring Car Championship and – in 1980 and 1981, driven by Win Percy (born 1943) – the British Saloon Car Championship.

If our earlier revelation that there was a rotary-engined Lada Classic came as a surprise to you, you might be even more amazed to learn that Lada pulled the same trick with the later Samara.

The Samara was introduced in 1984, hence its appearance at this point in the story, but rotary versions don’t seem to have arrived until the following decade. Production was once again low, but more examples were bought by private customers, and the power output is widely quoted at a rather impressive 140bhp.

The second RX-7 replaced the first in 1985. As before, it was essentially a coupe (though this time round a convertible was also available), and its styling to was similar to that of the earlier car, but certainly more modern and perhaps a little less distinctive.

Turbocharging, briefly available in Japan during the first generation, became more common. Several power outputs are quoted, but Mazda itself says that the highest was around 200bhp, giving the car a top speed of around 150mph and a 0-62mph time of six seconds.

The final Cosmo, introduced in 1990 and sold only in Japan, was a Mazda from its hat to its socks, but was marketed under the company’s short-lived Eunos brand. It was the first Wankel-engined production car with three rotors (the Mercedes C 111, as you’ll remember, was a prototype), and it had twin turbochargers.

Maximum power was officially 276bhp, though this may have been due to the ‘gentleman’s agreement’ among Japanese manufacturers at the time that none of them would quote a higher figure. The Cosmo was also the first production car to be equipped with GPS-enabled satellite navigation.

The 787B was the last in a series of Group C racing cars, best known for winning the Le Mans 24 Hour race in 1991. Contrary to the received wisdom about rotaries, it wasn’t especially fast (though it certainly sounded like it), but it was very reliable, qualifying poorly but soldiering on while the opposition hit trouble.

All three examples finished in the top ten, and the one driven by Bertrand Gachot, Johnny Herbert and Volker Weidler beat the second-placed Jaguar by two laps. It was the first – and, until 2018, the only – Le Mans victory by a Japanese car. The regulations were changed to allow only piston-engined cars from 1992, so this is also likely to be the only time a rotary will ever win the race.

The final RX model of the 20th century shared the twin turbocharging of the slightly earlier Eunos Cosmos, but unlike that car it had the normal two rotors rather than the exceptional three. The power output nevertheless reached the same 276bhp, at least in later versions sold only in Japan.

The engine was a highly developed version of one Mazda had introduced in the 1970s. As a new century approached, it was becoming increasingly difficult to make it meet emissions regulations in various parts of the world. For the next RX, Mazda would have to come up with something new.

There are many cases of people around the world of people fitting rotary engines into MX-5s, but Mazda itself has never done this – at least in a version available to the public. In 1993, however, it did create a development model of this type which used hydrogen rather than petrol as a fuel.

Since most of the exhaust from a hydrogen-fuelled vehicle consists of water, the traditionally poor emissions of a rotary immediately become unproblematic. The difficult part is storing the hydrogen in a car as small as this one. This couldn’t be resolved, so the hydrogen rotary MX-5 remained an interesting but impractical experiment, though it was probably never meant to be more that anyway.

The last of the RX models, and the only one sold in the 21st century, was a four-door coupe with a new development of the rotary engine known as Renesis, which won the overall International Engine of the Year award in 2003. The car handled exceptionally well, but even Mazda’s best efforts to keep exhaust emissions under control were not enough, and production was brought to a halt in June 2012, after just under 200,000 examples had been built.

A dual-fuel RX-8, capable of running either on petrol or (with a devastating effect on performance) hydrogen, was available for a few years, but only on a lease basis.

Also known as the Mazda 5 and Ford i-Max, the second-generation Premacy was an MPV/minivan usually powered by a petrol or diesel engine. A very small number were made using the petrol/hydrogen rotary also found in the RX-8, though this time it was connected to an electric motor as part of a hybrid powertrain.

As with the equivalent RX-8, the Premacy was offered only on a lease basis, and never sold outright to customers.

The e-tron concept version of Audi’s smallest hatchback was an electric vehicle with a tiny single-rotor engine which acted as a range extender when the battery charge fell below a certain level. It was never put on sale, though we described it in 2010 as “genuinely exceptional”, and noted that, although our tester had not heard the rotary starting up during his brief run in the car, it had in fact done so four times.

The fact that Audi even attempted a project like this was historically appropriate. The present-day company (as opposed to the one of the same name which did not survive beyond the 1930s) is partly a successor to NSU, the first manufacturer to put a rotary car into production.

Mazda began leasing an all-electric version of its 2 hatchback, known in Japan as the Demio EV, in 2012. A year later, it revealed a prototype which had a single-rotor engine acting as a range extender.

The principle was, of course, exactly the same that Audi had used in the A1 e-tron concept, though we reported that the Mazda engine was considerably louder than the Audi one. In any case, the range-extended 2 came no closer to full-scale production than the A1 had.

After the previously-mentioned attempts to make a rotary range extender viable for production, Mazda has finally taken the step with the MX-30 crossover. As intended, the single-rotor unit allows the vehicle to travel much further between battery charges.

This is likely to go down well in the United States, where the regular MX-30 (currently sold only in California) has the smallest range of any commercially available EV, according to US Environmental Protection Agency.