How Do Mazda Rotary Engines Work?

Wankel engines were invented in the early 1960s by Felix Wankel, a German engineer. As time moves on, turbocharging has been added and displacement has been increased. Mazda rotary engines have a reputation for being weak in fuel efficiency and strong in powerful given their small size. Between 1967 and 1977, the engine was a series with NSU and Citroën.

Wankel engines geometric are classified by radial size, depth, and offset. Most Mazda produced Wankel engine variants have a common a single rotor radius, 4.1 in, with a 0.59 in crankshaft offset. The only engine to vary from this pattern was the 13A, which used a 4.7 in rotor radius and 0.69 in crankshaft offset.

The 40A was Mazda’s first foray into Wankel engines. However, production sizes were small in quantity. The 40A was a wonderful experiment for Mazda’s engineers. Unfortunately, problems rapidly presented themselves. This design suffered from heavy oil consumption and “chatter marks” in the housing. The cause of the chatter marks was the tip-seal vibrating while heat-resistant rubber oil seals on the sides of the rotors solved the oil consumption problem. The 40A had a rotor radius of 3.5″, an offset of 0.55″, and a depth of 2.3″.

10A

Mazda’s first rotary engine production was the 10A series. Appearing in 1965, the 10A was a two-rotor layout. The chambers displaced 30.0 cu in. It had the common rotor dimensions with a 2.4″ depth. The rotors were cast iron. The aluminum/carbon apex seals fixed the aforementioned chatter mark problem.

0810, 0813, & 0866

The 0810 was the first 10A engine and used in the Series I Cosmo. The 0810 was customized for the Nürburgring racing Cosmos. These engines respectively had a butterfly valve in place of both sides and peripheral located intake ports for low and high RPM use. In July 1968, the improved 0813 engine in the Series II/L10B Cosmo. It was similar to the 0810 in build design. The 1971 0866 model was the last of the 10A family. This variant produced fewer emissions. REAPS (Rotary Engine Anti Pollution System) was the name Mazda gave its technology. Gross output was 105 hp at 7000 rpm and 135 Nm at 3500 rpm.

Mazda 12A rotary engine
Turbocharged 12A installed in Mazda Cosmo

13A

Mazda then started working on a single rotor engine that could displace 22 cu in. It had a two-rotor layout, with the individual chambers displacing 40.0 cu in. This was the only engine produced with different rotor dimensions: Radius was 4.7″ and offset was  0.69″, but depth remained the same as the 10A at 2.4″. Lastly, it had an integrated water-cooled oil cooler which differed from the previous engines.  The 13A produced 126 hp and 172 Nm.

The 12A is a stretched version of the 10A: the radius of the rotor stayed the same, however, 2.8″ was added to the depth. They maintained the two-rotor layout; with the added depth allowed the individual chambers to displace 35.0 cu in.

In 1974, a new manufacturing process was tried and successfully used to strengthen the rotor housing. The SIP (Sheet-metal Insert Process) implemented the use of a sheet of steel with a chrome-plated surface. In 1982, a 12A turbo-powered Cosmo coupe featured “semi-direct injection” into both rotors at once. It was used in the HB Cosmo series until 1989. However, during that time it gained a reputation as a thirsty engine.

The 12B was a product of 1974. The 12B was an engine that was produced specifically for the Mazda RX-2 and the RX-3. With greater reliability than it’s predecessors, it was given a single distributor.

Wankel rotors of 13B engines
Wankel rotors of 13B engines

13b

The most widely manufactured rotary engine was the 13B. For over 30 years Mazda used it as the foundation for the rotary engines to follow. In short, it was merely an elongated variant of the 12A. It was a two-rotor layout, with the individual chambers displacing 39.9 cu in.

RX-7

From 1985-1992, the 13B was used in the RX-7 FC. It vanished from the US market in 1995, when the US-spec RX-7s sold out. In Japan, the engine continued to be used from 1972’s Mazda Luce/RX-4 through 2002’s RX-7.

The Wankel engine with the 13B-RESI (Rotary Engine Super Injection) was when a tuned intake manifold was added for the first time. The Bosch L-Jetronic fuel injection was also used in the RESI engine. Output improved, 135 hp and 180 Nm.

The second-generation RX-7, much like the 12A-SIP, was bent with a variable-intake system. Christened DEI, the engine was given four-injector electronic fuel injection as well as both the 6PI and DEI systems. Total output is up to 146 hp at 6500 rpm and 187 Nm at 3500 rpm.

The 13B-T was, in 1986, turbocharged. Returning to the four-port intake layout, Mazda chose to give it the 6PI engine’s newer four-injector fuel injection. The output is rating is 185 hp at 6500 rpm and 248 Nm at 3500 rpm for the engines manufactured between ’86-’88.

The 13b series included the 13B-T, 13B-RE, 13B-REW. Similar to the sequential turbos used with the 13B-REW on the FD RX-7, the consecutive turbos had a large primary with a smaller secondary turbo.

Production Mazda Renesis engine in the Mazda Museum
Production Renesis engine in the Mazda Museum

RX-8

The Renesis engine – also 13B-MSP (Multi-Side Port) – which first appeared in production in the 2003 Mazda RX-8

As the 1970s fuel crisis struck, Mazda fully committed to the Wankel engine. By 1974, the company had eliminated most piston engines from its product lines. In the 1980s, Wankel engines were constrained to just use in sports cars, specifically the RX-7 and the Cosmo. All other Mazda vehicles had piston-gasoline or piston-Diesel engines. The company had continued production of Wankel engines since the mid-1960s and was the only manufacturer of Wankel-powered vehicles when the RX-8 was pulled from production in 2012.

RX-9

Mazda’s CEO, Takashi Yamanouchi, made it clear in 2011 that as long as he is involved with the company it will remain committed to producing rotary engines.

The rotary engine in recent years has been making a return. However, it is being reborn in the form of an electric car. It was marked to go on sale as the rotary-supported EV. I have had little luck in finding out if COVID-19 has affected the release of the 2020 RX-9.

At the announcement, Mazda further brought to light that the rotary engine would be able to run on gas. Which left people speculating whether Mazda would offer compatibility with other fuels at some point.

Mazda brought to light the rotary engine’s high power output partnered with its smooth running and small package and smooth operation neglected to say anything else definite about the vehicle or its engine. It also revealed that the range-extended vehicle could be used as a source of electricity when the power grid was down.

About Nishal Singh

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Car enthusiast since before I could drive.

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