Rotary engines made their biggest impact in Mazda sports cars, but a recent episode of "Jay Leno's Garage" delves into the rotary's earlier history.
Before it was popularized by Mazda, the rotary engine entered production with German automaker NSU (an Audi predecessor). The NSU Spider launched in 1964—three years before Mazda launched its first rotary car, the Cosmo 110S. One of those early NSU rotary cars is now part of Jay Leno's collection.
The rotary engine was invented by German engineer Felix Wankel and then licensed to automakers. It gets its name from the fact that, instead of pushing pistons, the energy from the combustion of fuel and oxygen is used to spin a rotor (or sometimes two, as was the case with later Mazda engines).
The rotor has a triangular shape but is mounted in a roughly round housing. The corners of the triangle are designed to seal against the housing (something that proved troublesome for engineers to achieve) allowing open spaces on the sides to serve as the combustion chamber. The fuel-air mixture (ignited by just one spark plug in the NSU) pushes against the sides of the rotor, spinning it.
The advantages of rotary engines were smooth operation and compact size. The NSU Spider's engine is so small that it sits below the rear luggage compartment, giving this convertible both a conventional trunk and a front trunk that help make up for its small size. The air intake is located on the rear trunk lid; air is directed down into the engine through a pipe in the trunk.
Disadvantages included higher oil consumption than conventional piston engines, and a self-destructive eagerness to rev. The NSU can easily rev to 8,000 rpm, Leno notes in the video, but that will wear out the rotor's seals. The tachometer even has a green zone ending at about 5,500 rpm to encourage more conservative driving behavior.
The NSU Spider was also fairly expensive for its time. It cost around $3,500 in 1964, more than other small sports cars like the MGB. And it only had 54 hp, sent to the rear wheels through a 4-speed manual transmission. Even with the Spider's roughly 1,500-pound curb weight, that made for a driving experience that required a bit of patience.
Rotary engine
After building a rotary sedan called the R080, NSU was acquired by the Volkswagen Group in the late 1960s and folded into what became Audi.
Rotary engines lived on, with General Motors and Mercedes-Benz experimenting with them in the 1970s and Mazda making them a regular feature in its lineup, notably in the RX-7 and RX-8 sports cars. The rotary-powered Mazda 787B became the first Japanese car to win the 24 Hours of Le Mans in 1991, but Mazda rotary production eventually ended in 2012.
Mazda announced the return of the rotary engine early this year, albeit as a range extender in a new R-EV version of the MX-30 electric crossover. The MX-30 R-EV won't be coming to the U.S., but Mazda unveiled an electrified rotary concept called the Iconic SP at the 2023 Tokyo auto show. That should keep hopes for the return of the rotary sports car alive.