Mazda rotary engines have a reputation for being relatively small and powerful at the expense of poor fuel efficiency.

As Wankel engines became commonplace in motorsport, the problem of correctly representing their displacement for the purposes of competition arose.

Although never produced in volume, the 40A was a valuable testbed for Mazda engineers, and quickly demonstrated two serious challenges to the feasibility of the design: "chatter marks" in the housing, and heavy oil consumption.

Hollow cast iron apex seals reduced vibration by changing their resonance frequency and thus eliminated chatter marks.

The Sheet-metal Insert Process (SIP) used a sheet of steel much like a conventional piston engine cylinder liner with a chrome plated surface.

The new "REST" process created such a strong housing, the old carbon seals could be abandoned in favour of conventional cast iron.

Applications: The 13B-RE from the JC Cosmo series was a similar motor to the 13B-REW but had a few key differences, namely it being endowed with the largest side ports of any later model rotary engine.

Approximately 5000 13B-RE optioned JC Cosmos were sold, making this engine almost as hard to source as its rarer 20B-REW big-brother.

The turbos were operated sequentially, with only the primary providing boost until 4,500 rpm, and the secondary additionally coming online afterwards.

[15] Output eventually reached, and may have exceeded, Japan's unofficial maximum of 280 PS (206 kW; 276 hp) DIN for the final revision used in the Series 8 Mazda RX-7.

A version of the 20B known as the "R20B Renesis 3 Rotor Engine" was built by Racing Beat in the US for the Furai concept car which was released on 27 December 2007.

[18][19] The first Mazda racing four-rotor engine was the 13J-M used in the 1988 and 1989 (13J-MM with two step induction pipe) 767 Le Mans Group C racers.

[20] In Group C and GTP this engine was replaced by the R26B, but continued to serve on in various Mazda supported entries in other championships around the world.

These championships included, but were not limited to IMSA's GTO and WSC Classes, and the Wesbank Modified Saloon Series.

It was designed to reduce exhaust emission and improve fuel economy, which were two of the most recurrent drawbacks of Wankel rotary engines.

It is naturally aspirated, unlike its most recent predecessors from the 13B range, and therefore slightly less powerful than Mazda RX-7's twin-turbocharged 13B-REW which develops 255–280 hp (190–209 kW).

Mazda changed the apex seal design to reduce friction and push the new engine closer to its limits.

These and other innovative technologies allow the Renesis to achieve 49% higher output and reduced fuel consumption and emissions.

[28][29] This is because although a 2-rotor wankel with 654 cc (39.9 cu in) chambers displaces the same volume in one output shaft rotation as that of a 1.3L four-stroke piston engine, the wankel will complete 2 full combustion cycles in the same amount of time that it takes the four-stroke piston engine to complete 1 combustion cycle.

The unmodified 13B-MSP Renesis Engine has a weight of 112 kg (247 lb), including all standard attachments (except the airbox, alternator, starter motor, cover, etc.

Also known as the Renesis II, made its first and only appearance in the Mazda Taiki concept car at the 2007 Tokyo Auto Show, but has not been seen since.

The 8C is a single rotor with a radius of 120mm, a depth of 76mm, using 2.5mm apex seals, and displacing 830cc making up to 75 hp (55 kW) at 4700rpm and 116 Nm (85 lb-ft) at 4000 rpm.

[33] It has a higher compression ratio of 11.9:1 and the first instance of Gasoline direct injection in a production rotary engine, which improves fuel economy by as much as 25%.

[35] Changes have also been made to decrease the weight of the unit such as using aluminium side housings, which saved 15 kg (33 lb).

Mazda last built a production street car powered by a rotary engine in 2012, the RX-8, but had to abandon it largely to poor fuel efficiency and emissions.

Mazda officials have previously suggested that if they can get it to perform as well as a reciprocating engine they will bring it back, to power a conventional sports car.

"[38] In November 2016, senior managing executive officer of Mazda research and development Kiyoshi Fujiwara told journalists at the Los Angeles motor show that the company would launch its first EV in 2019, and that it was likely to incorporate a rotary engine, but that the details were still "a big secret."

[39] In October 2017, Fujiwara told journalists that they were still working on a rotary engine for a sports car, that will potentially in some markets be with hybrid drivetrains, but both will have distinct powertrains from Mazda's first EV, which will be released in 2019/20.

"...some cities will ban combustion, therefore we need some additional portion of electrification because the driver can't use this rotary sports car.

"[40] In 2021, Mazda announced that the upcoming plug-in hybrid variant of the MX-30 would feature a new rotary engine that acts as a range extender to recharge the batteries, but not to power the wheels.