The intricacies of the defunct Wankel rotary engine

A basic dictionary definition gets us halfway to explaining a rotary engine: a rotary motion is essentially something revolving around a center axis. In this case, a triangular rotor is spinning around an output shaft, which leads us to the next question - so, what is a rotary engine? The rotary engine has one thing in common with the traditional piston engine: internal combustion, and that's about it. Unlike a conventional internal combustion engine, which has cylinder banks, rods, a crankshaft, and pistons, a rotary engine consists of these three essential parts:

There are other components, like an intake and outlet port and spark plugs to ignite the fuel, but a rotary engine only has these three major components, which is part of what makes it so attractive. In trying to answer the question, "How does a rotary engine work?", the easiest way to explain it is as follows. Imagine a side-on diagram in the shape of a barrel. Inside the barrel-shaped (oval) combustion housing, there are two or three triangular rotors. The open spaces between the rotors and the housing are known as chambers. As with a typical car, fuel and air are mixed and ignited by a sparkplug, moving the rotors around a fixed output shaft. The rotors and output shaft are connected, which supplies power to the wheels. Every other engine configuration, including the inline, V, VR, and W configurations use what we know as a traditional piston.

A rotary engine's specifications can be misleading. It's small, but it packs a punch. Well, at least in the horsepower department. The last production car to use a rotary engine was the Mazda RX-8. The engine specs for the RX-8 are as follows:

As you can see from the specifications above, you can't rely on engine displacement to estimate the power output. A 1.3-liter traditional piston engine would struggle to deliver 100 hp, but a similarly-sized rotary engine packs a 232 hp punch. And without the help of forced induction. The low torque output is also a mainstay of the rotary motor.

Usually, we categorize engine types according to size, number of cylinders, and engine configurations. Since the rotary engine is less complex, most production vehicles had two or three triangular rotors. Both the Mazda RX-7 and RX-8 had a 2-rotor layout, for example. There have been engines with more rotors than that, but these units were most often once-off builds for racing cars.

The main difference between rotary engines is in the cooling department.

The first rotary engine was designed by Felix Wankel in 1951. That's why rotary engines are also known as a Wankel motor, or more formally, the Wankel Rotary Engine. The design was then perfected by a man called Hanns Dieter Paschke. Wankel's version of the rotary was codenamed DKM. In his version, the housing and rotor spun on separate axes. It could rev much higher, but the complexity made it unviable from a mass-production point of view. Looking at a cutout of the DKM, you can see why. The entire engine would have to be disassembled to change a simple sparkplug. Paschke introduced the fixed housing with intakes, outlets, and spark plugs on the outside. According to legend, Wankel wasn't happy about this. He wanted to build racecar engines, while Paschke's focus was on simplicity.

Both men were employed by NSU Motorenwerke, who signed various licensing agreements with well-known automotive manufacturers like Nissan, Porsche, Mercedes-Benz, and even Rolls-Royce. Only one manufacturer chose to mass-produce the rotary engine over an extended period, and as you've probably guessed by now, it's Mazda. Mercedes-Benz deserves a special mention for the C111, though it never went past the concept phase. Most engines never made it past the initial test phase.

Mazda's first batch of rotary-engined cars was a flop. The Cosmo 110S was assembled by hand, and Mazda cut it from the line-up in 1972. Less than 1,500 were made. The Cosmo name soldiered on, but with traditional inline four-cylinder power.

The rotary engine only returned with the introduction of the now-famous RX-7. The third-generation twin-turbocharged model is considered an icon these days. It had a 1.3-liter engine, spurred on by a horribly complex turbocharging system. One turbocharger kicked in at 1,800 rpm, while the second took over at 4,000 rpm. This twin-turbo system was widely adopted in recent years, but back in 1992, it was mind-blowing. Mazda was able to extract 276 hp and 231 lb-ft of torque from a 1.3-liter motor. Even though the RX-7 won multiple awards, production was limited to less than 69,000 units. It was only really appreciated after its demise. Earlier generations are pretty easy to find for less than $10,000. A decent third-generation used Mazda RX-7 starts at around $50,000 these days.

Mazda tried once more with the RX-8, but it was not to be. This brilliant little car had its upsides, like revving to 8,500 rpm and sharp handling characteristics. On the downside, it was expensive to maintain, thirsty, and had notoriously frail electronics. Will there be another Wankel car? It's doubtful. Mazda has moved on to turbocharged four-cylinder engines and will launch its first electric car (MX-30) next year.

If you're asking 'what cars have rotary engines' today, you'll be disappointed to know there are no current examples to cite, and the aforementioned older Mazdas are the most famous. There are a few other examples of rotary-engined cars worth mentioning, but all of them never made it past the concept phase.

The rotary engine had a few things counting in its favor, but there were too many other factors that outweighed these. Pros and cons of the rotary engine can be summarized like this:

No. The Mazda RX-8 was the last car to use it. There are currently no plans for a new rotary engine.

It depends on the application, but it's worth stating that a piston engine is more efficient and requires less attention even though it has more moving parts. Rotary engines were always better suited to speed due to their high-revving nature, but even then, they were let down by a low torque output.

Yes. An angry vacuum cleaner is the best way to describe it. Because so much unburnt fuel is expelled into the exhaust system, rotary cars also tend to pop and bang more than the average JDM car meet.

Gerhard knew from a young age that he wanted to be an automotive journalist. He completely disappointed his parents by completing degrees in communication and English, as well as diplomas in graphic design and film and art appreciation. He later interned at various automotive publications, before landing a permanent position at a newspaper. He became the editor within two years, after which he landed a job as the deputy editor at a national publication, where he spent eight years traveling the world, driving, and writing. In his current role as senior editor, he writes news, reviews, scripts, and opinion pieces. When he’s not supposed to be working, you’ll probably find him working. When he’s forced to take a break, you’ll find him at the movies, or behind the wheel of a ‘92 NA Miata called Kimiko.