Mazda has always known to be an experimental company. It’s a carmaker that’s not afraid to push the envelope, and this is perfectly demonstrated in their development history. Even now, they’re the ones leading the charge at keeping internal combustion engine alive with their Skyactiv-X lineup of engines.
However, nothing Mazda makes today can quite compare to their stint with the rotary engine. Nowadays, Mazda is hinting at reinvolving themselves with hydrogen-based rotary engines. But back then it had put all their main interests in rotary engines.
It wouldn’t be far fetched to say that Mazda believed rotary engines to be the best alternative after reciprocating piston engines. And it’s fair to believe so too, as Mazda has single-handedly pushed the rotary engines to the mainstream.
Without Mazda, the Wankel rotary engines would’ve likely remained largely unknown and foreign to many. It’s Mazda’s unwavering effort to differ from the rest of the market that expanded rotary engines to the state it is today. Even today, the rotary engines garner a sizable fanbase, simply because there is no alternative.
Nevertheless, there are reasons that rotary engines fail. And while Mazda has produced dozens of different rotary engines, not all of them were successful. In fact, it’s fair to say that their latest volume-production rotary engine, the 13B-MSP (RENESIS) put the final nail in the coffin for future mass-production rotaries.
That said, frequent trials and learning from the results mean that Mazda must’ve gotten it right once for it to persevere with rotary engines as a whole. Look at Porsche, who has made the rear-engine rear-wheel driven 911, a seemingly daft idea, work.
For Mazda, this came in the form of the 13B engine. It’s the most widely produced rotary engine by far, and for good reasons. The 13B engine struck it just right, providing a fine balance between power, reliability and affordability.
Prior to the miraculously successful 13B engines, Mazda never really stuck with a single design for long. It’s fair to say that its predecessor is the 12A engine. It’s the first rotary engine that Mazda found worthy as an alternative powertrain for their production cars.
It’s also this engine that propelled the initial concept of the Rotary Experiment (RX) cars. Little did Mazda realise that they were on to a hit. Its first success came in the form of the RX-3, otherwise known as the Savanna.
The world, and Mazda, were quick to realise the main advantages of the rotary engine – its diminutive dimensions and lightweight. And for the time, the 12A engines, despite displacing just 1,146 ccs, were remarkably potent.
In the RX-3, the engine would produce right around 130 horsepower and 156 Nm of torque. More importantly, the small displacement and dimensions allowed Mazda to design the RX-3 around Japan’s dimensions regulations.
This allowed buyers of the RX-3 to afford a cheaper annual road tax price. The 12A engine would produce more power than its inline peers, while not being penalised by the higher 1.5-litre tax bracket denoted by the Japan government during the time.
Combined with the stylish muscular coupe styling of the RX-3, Mazda had a hit on their hands. In fact, the RX-3 was so successful that it made up the majority of the rotary engine sales back then.
Even when it came to the races, the RX-3 is a winning formula. It was a featherweight and powerful for a naturally aspirated 1.2-litre. In fact, it was one of the first few cars well-sorted enough to compete against the Nissan Skyline back in the 1972 Japanese Grand Prix. Furthermore, it was markedly robust pitted against domestic peers in Australia and the US.
Developing the 13B Engine
Mazda saw the purpose of a more powerful, yet more efficient rotary engine. For Mazda, this meant increasing the displacement of the engine while incorporating newer, emissions-friendly technology. It would gon on and dub these engines the 13B.
Perhaps without Mazda anticipating it, the 13B ended up being their most successful design. It’s the most widely produced rotary engine in the world. Despite the nomenclature, it has nothing to do with the 13A engines, which displaced the same, but with different dimensions.
The 13B is actually based off the 12A engine. To extract more power, Mazda developed thicker rotors which elongated the entire housing. Each 13B chamber displaced 654cc, so the 13B ended up being a 1,308 cc 2-rotor engine.
Crucially, the 13B engine was developed with the US EPA Muskie Law standards in mind. Because most RX-3 sold in the US, Mazda knew that this was a massive market that yearns for better fuel economy without strangling power. In fact, while most car manufacturers reckoned that complying with the Muskie Law was impossible, Mazda managed it with the 13B.
13B AP Engine
The first car to be powered by the 13B engine is thus the Luce AP, otherwise known as the RX-4. It was a car that took advantage of the 13B’s low weight and decent output to market itself as both luxurious and sporty. The AP stands for anti-pollution, and the extra displacement was necessary to offset the power losses from the 12A’s emissions regulation device.
With that said, the 13B AP isn’t exactly as well-documented as the other 13B engines. It’s an engine perhaps most well-known for powering the revered Mazda Rotary Pickup (REPU) though, as that remains to be the sole pickup truck to be powered by a rotary engine even today.
Because the main pollutant of a rotary engine is excess hydrocarbon from unburnt gas, Mazda devised a method to improve upon this. This is dubbed by Mazda as a thermal reactor, a primitive emissions device that’s installed right at the exhaust of rotaries of this era.
Essentially, imagine it as a jet engine powered from the 13B’s exhaust gas. It’s double-walled and insulated to maintain efficiency. It begins to function at 600-700 celsius, where the hydrocarbons can combust completely. An air injection pump is utilised to feed cool air around the reactor chamber to prevent overheating.
The thermal reactor was ingenious back then, as it enabled Mazda to clear the US EPA Muskie Act test. By now, Mazda was also working on developing an advanced catalytic converter. The thermal reactor system remained in use until 1980 though. Nowadays, it’s seen as a bit of a nuisance and deleted in the hands of enthusiasts.
However, the 13B AP is really just a 12A engine with extra displacement. It faced one big issue that plagued every carmaker back in the 70s – the oil crisis. The soaring oil prices meant that fuel efficiency was more important than power, and the 13B performed poorly in fuel efficiency terms.
Mainly, the underperforming fuel economy figures were due to fundamentally flawed design in the 12A. It also used a carburettor system which just can’t meter and deliver fuel accurately and effectively enough for the increasingly stringent emissions law and consumer demands.
The FB3S RX-7 with the 12A Engine
Following the formula of the RX-3, Mazda took note of what made the RX-3 work. Since nearly half of all the RX-3s sold are coupe models, this factored into the design philosophy of the RX-7. A sleek, lightweight and compact pure sports car.
Introduced in March 1978, the RX-7 Savanna, or FB3S, is the direct successor of the RX-3 Coupe. It mimicked everything that made the RX-3 Savanna a popular option amongst the Japanese, compact size, low weight and balanced handling.
The FB3S RX-7 still used the same 12A engines with roughly the same output. However, the minimal 1,100 kg weight enabled a sub-10 second 0-60 mph time. Most importantly, the dimensions of a 12A allowed the engine to be placed behind the front axle. This front-mid engine layout would become the staple of RX-7 design.
While the 12A in the RX-7 produces less power than the older 12As, this was due to the emissions control strategy used by Mazda to cope with the regulations. This was all part of the Mazda ‘Phoenix Project’ to revitalise the rotary engine’s image as a viable reciprocating piston alternative. Compared to earlier 12A, this ‘lean burn’ 12A managed just about 100 horsepower and 135 Nm of torque.
This necessitated improvements to the 12A’s combustion behaviour, carburettor design and also the world’s first rotary engine catalytic converter system. It also involved an improved ignition system and additional split air injection valve for the two-pellet catalytic converter.
All of the above improvements also allowed the 12A to operate at a leaner fuel mixture without impacting its NOx emissions. This was marketed by Mazda as a lean-burn rotary engine, which by today may be confused by some as a system akin to modern stratified fuel injection engines. This emissions-conscious 12A engine was known as the 4-port and was used in the Series 1 (SA) and Series 2 RX-7s.
Finally, some later Series 2 RX-7s (referred to as the FB) received a further refined 6-port 12A engine. The 6-port 12As featured 2 additional induction ports that functioned at around 4,000 rpms. The 6-port 12A also incorporated an exhaust gas recirculation system to further improve emissions. The carburettor was also improved to an auto-choke unit. Power is bumped up slightly to 115 horsepower.
With all that said, despite Mazda’s engineering efforts, the 12A just didn’t produce enough power to entice the higher end crowd. This is when Mazda developed a turbocharged variant of the 12A. It’s only found in the final Series 3 RX-7s, the Luce, and the Cosmo starting from late 1982.
This 12A served as the basis for future RX-7 engines, as it proved that a turbocharger designed for the purpose can be very beneficial without heavily compromising fuel efficiency and emissions. The 12A turbo ditched the carburettors for electronic fuel injection. The compression ratio is reduced to 8.5:1 from 9.4:1 for turbocharging.
This engine also went through two iterations. The early versions used a bigger Hitachi HT18-BM turbocharger that yielded 160 horsepower and 224 Nm of torque. Later variants, however, used a revised, but smaller, HT18S-BM with revised turbine wheel design. The blades are better optimised for rotary engine exhaust pulse, and this is dubbed an ‘Impact Turbocharger’ by Mazda. Power is improved to 165 horsepower, but turbo lag is minimised and thus torque delivery is improved.
13B Engine Development
Learning from the 12A Turbo, Mazda went on to further develop the 13B engine. This materialised in the form of the 13B-RESI, an engine only used from 1984 to 1985 in the Luce, Cosmo and RX-7 (FB3S Series 3). You can identify the 13B RX-7s from the GSL-SE trim level.
The 13B-RESI (Rotary Engine Super Injection) is a naturally-aspirated 1.3-litre 2-rotor engine that produces 135 horsepower and 180 Nm of torque at just 3,500 rpm. It’s a big improvement over the earlier 12A models, so this is one of the ultimate
Most remarkably though is the improved fuel economy figures. Combined, the 13B-RESI is rated for approximately 25 mpg. Time for 0-50 mph is achieved in 6.3 seconds. The main changes from the 13B AP are found in the fuel delivery system and intake system.
The 13B-RESI utilises a Bosch L-Jetronic fuel injection engine with a single fuel injector located at the intake port of each rotor chamber. Without turbocharging though, the 13B-RESI utilises an early iteration of intake supercharging. It’s a two-level intake system to improve low-end output without impacting top-end power.
Of course, any keen Mazda fan would recognise this as an early iteration of Mazda’s variable intake system. It’s one of the best adopters of variable intake technology. In fact, the RENESIS engine nowadays has multiple stages of intake valve control to make the best out of the rotary engine’s intake characteristics.
Internally, these 13B-RESI engines only resemble the 13B AP engines. However, it features reliability improvements from Mazda better understanding the flaws of a rotary. Notably, Mazda implemented a high-flow oil pump from the 12A Turbo as well as an in-housing oil squirter near the air inlet.
Following the 1986 launch of the second-generation FC3S RX-7, Mazda needed newer and improved engines to power the car. The FC3S was initially available with two engines, the non-turbo 13B-DEI and the turbocharged 13B-T. At this point, the 12A engine was mostly phased out of use.
Mazda put more emphasis on a few key points of these new 13B engines. Mainly, Mazda intended for better output throughout the operating range, increase redline to enthrall drivers, improved engine response, better fuel efficiency, and reduce oil consumption.
Despite remaining a 1.3-litre naturally-aspirated 2-rotor engine, Mazda managed to extract more power out of the 13B-DEI. At 146 horsepower and 187 Nm of torque, even non-turbocharged RX-7s feel quick enough to entice regular consumers.
Improvements came mainly in improving combustion quality by revising the DEI’s intake and fuel delivery systems. The 13B-DEI employed two additional auxiliary ports, thus using a 6-port induction (6PI). It’s an innovation over the more primitive 2-level, 6-port induction system used in prior 12A 6-port engines.
Additionally, Mazda also incorporated a dual-fuel injector system in lieu of the single injectors found in early fuel injected rotary engines. Again, its an early iteration of modern dual fuel injector rotary engines.
Similar to newer rotary engines, there’s a set of smaller and larger injectors. The idea is that the smaller injectors provide better fuel delivery characteristics and atomisation at idle to low rpm range. The larger injectors can then supply the additional fuel required at the higher rev range.
Thus, stable combustion can be maintained at low speeds. This means the engine emanates less excess unburned hydrocarbon and thus returns cleaner emissions. It’s a system that is now commonly incorporated in rotary engines.
A few years later in 1989, Mazda introduced the facelifted Series 5 FC3S with an improved variant of the 13B-DEI. This new 13B-DEI touts better engine management, revised intake manifold and 9.7:1 higher compression ratio as well a lightened rotors. Power output is improved to 160 horsepower and 190 Nm of torque.
However, despite the improved output of the naturally aspirated engines, the turbocharged FC3S are what really captured international buyers attention. Previously, turbocharged rotaries are a relative scarcity. In fact, turbocharging an originally naturally aspirated rotary is no simple feat.
The turbocharged 13B-T was one of the first widely accessible turbocharged rotary engines for the public. In its initial configuration, the 13B-T puts out 182 horsepower and 248 Nm of torque. These variants with the turbocharged engines are known as the RX-7 ‘GTR’.
In lieu of a 6-port design, the 13B-T actually reverted back to the more traditional 4-port intake design. The dual injector design remained in use though. Later Series 5 RX-7 ‘GTX’ utilises higher compression ratio at 9.0:1 along with other updates found in the non-turbo variants. The output is increased to a remarkable 200 horsepower and 265 Nm of torque.
The 13B-T engines are often praised amongst the rotary enthusiast community for responding positively towards aftermarket modifications. With flow improvements on the exhaust side, larger injectors and a programmable engine management system, it’s not difficult to make approximately 250 horsepower out of these engines.
Combined with the relative abundance of these engines, its a recommended alternative for those who intend to turbocharge their naturally-aspirated 12A or 13B engines. However, it is an early experimentation with turbocharged rotary engines by Mazda, thus the 13B-Ts had a few design flaws that limited its maximum output.
Regardless, if you’re looking for a turbocharged rotary engine, and isn’t looking to make big power, then these 13B-Ts engines are a good option other than the expensive 13B-REWs. The 13B-T also found its way into the Mazda HC Luce (or 929), among many other engines that Mazda opted to power their luxobarge.
In the late 1980s and early 1990s, carmakers in Japan were stepping it up in an arms race. Everyone was competing against their peers. Manufacturers would race to incorporate some genuinely cutting-edge technology into their halo cars. In this competition for one-upmanship, Mazda enjoyed the distinct advantage of being the only company offering rotary drivetrains.
For Mazda, their halo car was the JC Eunos Cosmo. It was Mazda’s ultimate display of luxury, showing the world that they’re capable of making a grand tourer that rivals Lexus. It’s also esteemed for being powered by the only production 3-rotor engine ever offered by Mazda, the 20B-REW.
However, the Eunos Cosmo was also offered with the comparatively modest 13B-RE. In fact, more Cosmos powered by the 13B-RE was sold than 20B powered Cosmos. It’s a sequentially turbocharged 1.3-litre 2-rotor engine producing 227 horsepower and 294 Nm of torque.
The Cosmo is especially noteworthy for boasting the first commercially-available sequential turbo rotary engine. To counteract the low torque nature of rotary engines, a Hitachi HT-15 primary and Hitachi HT-10 secondary provides an extra boost when needed.
In fact, such a system was efficacious for achieving the Eunos Cosmo’s vision – the epitome of a Mazda grand tourer. The Cosmo 13B-RE engine made its peak torque at 3,500 rpm, optimal for cruising on motorways. Boost is limited to a modest 8 psi.
The 13B-RE is often remarked to feature some of the biggest stock intake ports offered on the production 13B engines. It also sports an intake manifold with bigger runners. Though the 13B-RE is often dismissed for its inability to sustain high rpm operations and restrictive exhaust sleeves. Of course, it’s also as difficult to source as a 20B engine.
Alongside the 13B-RE’s development is the 13B-REW. This is the ultimate 13B engine that most people think about when they think of rotary engines. Powering the 1992 RX-7 FD3S, it’s also the most powerful stock 13B engine that Mazda makes.
Many parts are shared between the 13B-RE and 13B-REW. However, with some major differences, the 13B-REW actually makes a lot more power than the 13B-RE. In fact, during its initial launch, the 13B-REW would’ve put out 250 horsepower and 294 Nm of torque.
Rather than sizing two different turbochargers, both turbos on the FD3S are Hitachi HT-12s. With two identical turbochargers, Mazda staggers the charge air for better response. Basically, the primary turbo spools as a single first, feeding only minimal exhaust energy to the secondary turbo.
Only until the secondary turbo is fully ready then a flap opens to feed equal amounts of exhaust to it. It’s a decidedly impressive system given the constraints Mazda engineers worked with. However, its torque delivery is only semi-linear at best. For more on the sequential turbocharging system, read here.
By monitoring the boost levels, it’s overt that the boots go from 10 psi below 4,500 rpm, to suddenly dropping to 8 during 4,500 rpm before building back up to 10 psi all the way to redline. This famous 4,500 rpm transition is what often catches novice FD drivers off guard in the corners. It also earnt the RX-7 the reputation of being tricky to drive properly.
Mazda also made multiple key refinements to the 13B-REW for it to appeal as a true sports car engine. For one, oil pressure is increased despite sharing the same oil pump in the 13-RE. The rotor bearing is improved to a 9-window design. Exhaust sleeves are enlarged. The stationary gears are also strengthened.
Therefore, despite being a similar engine to the 13B-RE, the 13B-REW can sustain engine operations at 8,000 rpm, making it the definitive enthusiast’s rotary engine of choice. It’s also where the extra horsepower comes from. The output is eventually improved to 276 horsepower and 314 Nm of torque by the end of the FD3S’s life.
13b Engine Verdict
The 13B engines are an enduring staple in Mazda’s history as a whole. In fact, if it wasn’t for the 13B engines, it’s likely that Mazda won’t be as doted as they are now. The 13B-REW is one of the best rotary Mazda has produced. Along with the FD3S’s brilliant engineering and timeless design, it’s not hard to imagine why it’s so beloved.
It’s perhaps why many treat the RENESIS as a step back for Mazda. It’s illogical to say that when both engines are built at different times with different priorities in mind. That said, it can be argued that most Japanese car manufacturers have not quite outperformed themselves 2 decades back.
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