Everything You Need to Know About the Mazda 13B Rotary.

Few engines are as divisive as Mazda’s range of rotaries — it seems like enthusiasts either love them, or they hate them. Over the last five decades, these motors have powered everything from tiny classic sports cars to 26-seater buses, to some of the world’s greatest race cars. 

In this article, you’ll learn the story of the 13B — by far the most-produced rotary engine — including why people are obsessed with it, the best way to extract power from it, and much more.

In this article you’ll find:

  1. History of the 13B
  2. Why do people love the 13B?
  3. Where can you find the 13B?
  4. What’s the best 13B?
  5. Pros and cons of the 13B
  6. Tuning a 13B
  7. Porting a 13B
  8. Weaknesses of the 13B
  9. Getting the most from your 13B

A Brief History of Mazda’s 13B Engine

Mazda’s 13B rotary engine traces its roots back to the Wankel rotary engine design developed by German engineer Felix Wankel in the 1950s for manufacturer NSU.

Unlike traditional piston engines, the rotary uses triangular rotors mounted on an eccentric shaft and spinning in housings to compress and ignite the air-fuel mixture. This allows for smoother operation and high-revving potential, characteristics that would become synonymous with Mazda’s rotary lineup.

Mazda saw the potential of this revolutionary concept and, after licensing the design in the 1960s and pouring in huge amounts of research and development to overcome initial issues with reliability — especially concerning the apex seals — and refined it into a compact, lightweight, and high-revving production engine. This first road-going version was the two-rotor 1000cc 10A, being fitted to the original Cosmo sports car (L10A). 

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Credit: Just Cars

The following years saw improvements to the challenging design with its inherent reliability, efficiency, and emissions issues. After the bigger 1200cc 12A was unveiled, it wasn’t long before the even bigger 1300cc 13B arrived in 1973, fitted between the struts of Mazda’s RX-4 luxury coupe. 

A year later and the motor was being dropped into a range of different Mazdas, including the updated Cosmo (AKA the RX-5), the aforementioned Parkway bus, a pickup specific to the US market called the REPU, and even a rebadged Holden Premier. This original version of this motor is known as the 13B-AP, standing for ‘anti pollution’.

Moving forward to the mid-eighties, Mazda introduced the 13B RESI (Rotary Engine Super Injection) which powered the HB Luce and Cosmo, as well as the SA22/FB Series 3 RX-7. Besides moving to fuel injection, this motor also used a unique two-stage intake tract that helped give it a significant boost in power compared to the previous AP version.

Next, it was time for the 13B-DEI. This motor was used in the non-turbo FC3S RX-7s and added a new injection system that doubled the count of injectors from two to four — the second set only activating when needed. This, along with a newly revised intake tract, resulted in another step up in power and better round-town drivability.

For the turbocharged versions of the FC3S RX-7, Mazda introduced the 13B-T, which used lower-compression rotors, as well as the four-injector system seen in the DEI. These motors were the first to break the 200hp mark thanks to a new twin-scroll turbo and split intake manifold system. The 13B-T was highly regarded at the time as enthusiasts realised the potential of turbocharging the rotary engine.

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This was only heightened by the introduction of the FD3S RX-7 in 1993, which featured the most popular and highly-regarded twin-rotor Mazda engine — the fabled 13B-REW. This twin-turbo 1300cc motor helped the new RX-7 reach legendary status, even if the complex sequential turbocharger system was prone to failure. It was this motor that helped the rotary engine become more mainstream, and is today still the most popular 13B to use and modify for turbocharged applications.

It’s also worth recognising the similar 13B-RE, which was only used in the JDM Cosmo of the early 90s. This particular motor is desirable for enthusiasts due to its bigger side ports and injectors, amongst other minor tweaks. 

renesis

After a brief hiatus, the 13B returned in 2004 with the introduction of the 13B-MSP, also known as the ‘Renesis’. This naturally aspirated motor powered the RX-8 exclusively and went through multiple changes throughout its lifespan. While factory power levels were good considering the lack of forced induction, the Renesis motor suffered from various reliability issues and is not prized in the aftermarket due to the challenges of modifying it, and its lack of potential when compared to the previous 13B-REW. 

With the end of the RX-8 in 2012 came the end of the 13B lineage (unless something new comes along). Fuel consumption, emissions, and reliability issues eventually put the final nail in the coffin for this motor but with that said, it still remains extremely popular in the enthusiast and motorsport world to this day.

Why Do People Love the Mazda 13B?

In a world absolutely dominated by piston engines, Mazda’s series of rotary motors — particularly the 13B — stand apart for their unique operation, sound, and power delivery.

Few engines command as rabid and devoted a following as the Mazda rotary, especially in hot spots like Puerto Rico, Australia, and New Zealand, where aftermarket development has been non-stop over the last thirty years.

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The 13B has garnered a cult following due to its lightweight design, high power-to-weight ratio, and distinctive sound, often described as a pulsing “brap” at idle and a screaming “buzzsaw” at high RPMs. Nothing else sounds like a rotary engine, and that is a big draw card for a lot of people.

In motorsport circles, the 13B’s ability to rev freely and produce substantial power from a relatively small displacement has made it a popular choice in various racing applications. Its simplicity in design, with fewer moving parts than piston engines, also contributes to the appeal.

The 13B is also highly tunable, with options ranging from a screaming naturally aspirated build all the way up to 1500hp+ turbocharged drag applications. 

Despite its tarnished reputation in the wider community due to reliability issues (most of which are caused by poor tuning, engine building, and maintenance), the 13B’s devout fan base, OEM part availability, and large aftermarket industry make it the ideal motor for enthusiasts looking to make big power in a completely unique way. 

Where Can You Find Mazda 13B Engines?

The following is a list of each variant of the 13B engine, as well as the vehicles they powered over the years, starting in 1972 with the RX-4 and finishing in 2012 with the discontinuation of the RX-8.

13B-AP 

9.2:1 CR, 187-203hp, 168-171 lb-ft

  • 1972-1977 USDM/EU/AUDM/NZDM RX-4 (LA)
  • 1974-1977 USDM REPU (PA/SPA)
  • 1974-1977 JDM Parkway
  • 1975-1980 JDM Cosmo (CD)
  • 1975-1977 JDM Roadpacer (HJ/HX)
  • 1973-1978 JDM Luce Rotary (LA)
  • 1975-1981 JDM Cosmo (CD)
  • 1976-1978 USDM Cosmo (CD)
  • 1975-1981 EU/AUDM/NZDM RX-5 (CD) 

13B-RESI

9.4:1 CR, 135hp, 133 lb-ft

  • 1984-1985 JDM Luce (HB)
  • 1984-1985 JDM Cosmo (HB)
  • 1984-1985 USDM Mazda RX-7 GSL-SE Series 3 (FB/SA22)

13B-DEI

9.4:1 CR, 146hp-160hp, 138 lb-ft

  • 1986-1988 JDM/USDM/EU/AUDM/NZDM RX-7 Series 4 (FC3S) 
  • 1989-1991 JDM/USDM/EU/AUDM/NZDM RX-7 Series 5 (FC3S)

13B-T

8.5:1-9.0:1 CR, 185hp-200hp, 183 lb-ft

  • 1986-1991 JDM Luce Turbo-II (HC) 
  • 1986-1988 JDM/USDM/EU/AUDM/NZDM RX-7 Turbo-II Series 4 (FC3S)
  • 1989-1991 JDM/USDM/EU/AUDM/NZDM RX-7 Turbo-II Series 5 (FC3S)

13B-RE

9.0:1 CR, 230hp 

  • 1990–1995 JDM Cosmo (JC)

13B-REW

9.0:1 CR, 255-280hp, 217-231 lb-ft

  • 1992–1995 JDM/USDM/EU/AUDM/NZDM Series 6 RX-7 (FD3S)
  • 1996–1998 JDM/UKDM/AUDM/NZDM Series 7 RX-7 (FD3S)
  • 1999–2002 JDM Series 8 RX-7 (FD3S)

13B-MSP Renesis

10:1 CR, 189-238hp, 156-163 lb-ft

  • 2003-2012 JDM/USDM/EU/AUDM/NZDM RX-8 (SE3P)


What’s the Best Mazda 13B Motor?

There isn’t one single “best” 13B motor, as it’s dependent on its intended application. For example, are you planning to leave it stock or are you going for a big power build? Will it be naturally aspirated or forced induction? 

So, let’s start with natural aspiration. In this situation, your best bet is going to be the 13B DEI from the 1989-91 Series 5 RX-7 (FC3S). This is because it uses higher compression 9.4:1 rotors, and traditional ports (unlike the RX-8’s 13B-MSP), and can be fairly easily swapped into any car due to its simplicity. 

With the right modifications, the 13B-DEI can make over 200hp at the wheels — carbureted or injected. If you want to take things further, these motors can make 400hp+ NA and even higher but going that far will result in some fairly substantial compromises in regards to longevity, drivability, and comfort so doing this is more of a drag car application than anything else.

It’s worth noting here that the Renesis RX-8 engine, while on paper seems like a good choice, is a much more complex affair just to get running in a swap situation, let alone modify for bulk power due to its unusual side port arrangement and emissions controls. 

If you’re looking to buy an RX-8 or already have one then, absolutely, these engines can be modified — it’s just not going to be an easy road to go down. The series 2 cars from 2008-2012 are the ones to get as many improvements were made to the 13B-MSP (known as the Renesis II) in these cars. All examples of the Renesis II motor are six port, unlike some of the earlier versions, half of which were four-port as fitted to automatic transmission equipped RX-8s.

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If you’re looking at the turbocharged route, you can’t go wrong with either the 13B-RE from the Cosmo, or the easier-to-find 13B-REW found in the FD3S RX-7. These motors can make upwards of 400hp at the wheels before they need to be cracked open. With a simple street port, the right size turbo and supporting modifications, that figure can be pushed considerably higher before running into too much trouble.

Go further with a more aggressive porting like a bridgeport, a stud kit, upgraded seals, balanced rotors and the right fuelling and ignition, and these 13B-REW motors can make massive power — how much depends on your appetite for risk, what you want to do with it, what fuel you want to run, and how much you enjoy rebuilding rotaries! There are 13Bs out there (specifically in Australia and Puerto Rico) that are powering cars to mid-six second-quarter miles on methanol!

Known Weaknesses of the Mazda 13B Engine

Mazda’s rotary engines suffer from one of the worst reputations of any performance engine out there in terms of reliability — but the reality is a little more complex and many failures can be attributed to the builder or tuner, rather than the design itself. With that said, there are some weaknesses that need to be considered when working with a 13B. 

  • Factory apex seals are good, but brittle and can shatter, especially if carbon builds up due to a lack of hard driving
  • Very sensitive to detonation, ignition misfire, or lean conditions
  • Running hot for a brief period of time can wreck the motor

Pros & Cons of the Mazda 13B Engine 

Pros

  • Good aftermarket support
  • New crate engines and parts availability from Mazda
  • Capable of big power when built properly
  • Capable of high revs
  • Small size
  • Light weight
  • Simple design with few moving parts
  • Very smooth
  • Unique
  • Unmistakable sound

Cons

  • Poor fuel economy
  • Lacks torque
  • Premixing of fuel/oil is required if the factory oil metering pump isn’t being used, as is commonly the case for built motors
  • Sensitive to any ignition or fuel inconsistencies, as well as heat
  • Easy to flood
  • More frequent servicing and potential rebuild intervals

Porting a Mazda 13B

Anyone who has paid any sort of attention to rotary engines in the past will be aware that one of the main modifications an enthusiast tends to make when building a 13B is porting the housings. But what does that actually mean?

To put it simply, as we know, the rotary engine spins rotors on an eccentric shaft inside housings, and between these housings are “irons”, also known as “side plates”. 

Rotary Porting 05

Credit: Speed Academy


For all 13Bs except for the 13B-MSP Renesis, these plates feature intake ports that allow air in to be compressed, while the housings themselves host the exhaust ports through which gases flow out after the combustion process has taken place. On the RX-8’s 13B-MSP Renesis however, both intake and exhaust ports are located on the irons.

The bigger the ports, the more air can be allowed in, and the more exhaust gases can be extracted out. 

Porting can be thought of as similar to installing more aggressive camshafts in a traditional piston engine, especially as it produces similar results — the more extreme you go with it, the more power you’ll theoretically make higher in the rev range, but there will also be a corresponding drop in drivability and efficiency as a result. So, just like more lift and duration on a cam lobe opens a valve longer to allow more flow, so does increasing the port size. 

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There are a range of commonly performed porting styles:

Street Port

This is the mildest form of porting, designed to improve power without sacrificing reliability or drivability for street use. It typically involves enlarging the stock ports and reshaping them to allow more air to flow into the engine. This increases power across the rev range without severely impacting low-end torque or fuel efficiency. 

Bridge Port

In bridge porting, a “bridge” of metal is left between the original port and an additional, larger port to increase airflow. This modification creates more intake port area while still allowing the corner seal of the rotor to travel over the original port without falling out. This provides a significant increase in power, especially at high RPMs, but the idle gains its distinctive rotary “pulse” (which is a good thing for many people), and low-end torque is reduced. 

Half-Bridge Port

A hybrid between street and bridge porting. In half-bridge porting, the primary ports are opened up like in a street port, but a smaller bridge is added to give some of the benefits of a full bridge port. This offers a good balance between power and drivability. 

Extended Bridge Port

Sometimes also called a “J port”, this is a more aggressive form of bridge porting, where the bridge is extended further into the water jacket, allowing for even greater airflow. This extension means the water jacket needs to be filled/sealed with something like Devcon. The “J” shape of the port increases the duration of the intake, leading to higher RPM power gains. This further increases high-RPM power but sacrifices even more low-end performance and drivability. 

Peripheral Port

This is the most extreme form of rotary porting, where new intake ports are created directly in the rotor housing, bypassing the side ports entirely. Peripheral ports allow for maximum airflow into the engine. Peripheral porting delivers the highest power gains, especially at high RPMs, but creates a very rough idle and significantly reduces low-end torque. It also increases fuel consumption and emissions.

Semi Peripheral Port

Exactly what it sounds like, the “Semi PP” port involves a less aggressive peripheral port on the intake side and conventional side ports, which can be modified however the builder sees fit.

Tuning a Mazda 13B

While tuning a rotary engine is just like tuning any other combustion engine, there are some points that are worth knowing about and keeping in mind. 

First, reflashing the stock ECU isn’t a viable option when it comes to the 13B-powered RX-7 and Cosmo platforms. This means that an aftermarket standalone ECU is going to be the best option here — any modern standalone that features staged injection and the ability to run trailing split for ignition will do a great job. In fact, any four-cylinder-capable ECU will have more than enough injection and ignition drives to run a 13B.  

The RX-8, on the other hand, can be reflashed and there are a number of options out there to facilitate this, with many suppliers providing off-the-shelf tunes if needed.

Next, it’s extremely important to understand that rotary engines like the 13B are not what you’d call resilient engines when it comes to tuning. It sometimes only takes a single instance of detonation on the dyno to destroy an engine, so it pays to be extremely cautious, especially when adjusting timing. 

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The same goes for heat — when tuning the car, you’ll need to keep a close eye on the oil and coolant temperature, as it doesn’t take much time spent running hot to ruin a motor.

When tuning, a 13B tends to want richer AFR targets compared to a piston engine. This means that at idle, you should be aiming for an AFR of 13.5:1 to 14:1, and once at atmospheric pressure, around 11:1 should be the target. Once you get into boost, you should generally be looking for a richer AFR  than what you'd be aiming for with a piston engine. 

Generally, tuners tend to be very scared of using too much ignition timing, so they use almost none, which in turn creates massive heat in the exhaust. They then combat that with extremely rich mixtures. The reality is, if you get the timing where it needs to be, all of a sudden the engine doesn't need to be stupid rich to stay alive.

When it comes to injection timing, rotary engines are slightly more sensitive to it than a piston engine. That being said, this isn't where you're going to unlock an extra 100hp, so don't beat yourself up. Typical end of injection values of 130-200 at low rpm, and 330 at high rpm should have you in the ballpark.

In terms of modifications, the 13B works well in naturally aspirated or force-fed applications, obviously with substantially more power possibilities once a turbocharger is added.

A good NA street build using high-compression Series 5 FC RX-7 rotors should see an easy 200hp at the wheels with a decent street or bridgeport, intake, and exhaust. These motors can obviously be pushed harder with more aggressive porting, rotor tip clearancing, an obnoxiously bigger exhaust, proper engine management, and the right fuelling, but it’ll come at the expense of longevity, reliability, and comfort. 

A naturally aspirated 13B PP race motor, for example, is capable of 300+hp at around 10,000rpm. 

The RX-8’s 13B-MSP Renesis is in theory a good naturally-aspirated rotor, but its modification possibilities are limited without large investment, as Mazda actually did a great job with these motors right from the factory — up to 238hp at the flywheel for the later models using the improved “Renesis II” 13B-MSP engine. 

Unfortunately, there is no easy path to more bulk horsepower from this point that doesn’t involve stripping the motor down and porting and/or going the turbocharged route, which is a big can of worms to open.

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Moving on to forced induction, the 13B-RE from the Cosmo and 13B-REW from the FD3S RX-7 are going to be the best pick. These motors will make up to around 400hp at the wheels with the right supporting upgrades — ECU, fuel, intake, and exhaust. For context, our FD3S RX-7 project made 420hp at the wheels on factory ports.

Moving up in power levels is going to require the motor being opened up so a stud or dowel kit can be installed, as well as porting (streetporting provides a good level of compromise) and rotor clearancing. 

For clarity’s sake, stud and dowel kits are two similar methods of reducing or eliminating the motor flexing under load by essentially adding extra rigidity and clamping pressure to better and more evenly pull the housings and plates together. 

If this is done, and the right supporting modifications have been carried out — especially when it comes to turbo and injector size — the power possibilities are much higher. 

For example, the use of something like a Garrett G40-900 turbocharger sitting on an aftermarket exhaust manifold, and pushing through a big front mount intercooler should see 700hp at the wheels with the right fuelling (1700cc primary and 2600cc secondary injectors would suit this application).

From there, the sky really becomes the limit as turbo size can increase to massive proportions. 

With a big enough turbo, the right supporting modifications, and a switch to race gas or even methanol in drag car applications, the 13B can make absolutely ridiculous levels of power — well in excess of 1500hp at the wheels. Past this, a handful of companies, like PPRE, Mazdatrix, and PAC Racing, are even making billet housings, plates, eccentric shafts, and other internal parts pushing power potential even higher. 

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Before finishing up, a subject that needs its own discussion is the dreaded and sometimes misunderstood apex seal. Things aren’t exactly clear here as there’s so much conflicting information and experiences floating around. With that said, from our personal dealings, the stock Mazda carbon seals do a great job and are suitable for N/A and moderately powerful turbo engines. 

Ceramic seals are also a popular option in the aftermarket, and are most commonly used in high-output N/A race engines. These seal well and tend to last a long time … Until they don’t, at which point they’ll explode into a thousand pieces and obliterate everything inside the engine.

The final main choice are aftermarket steel seals. There is a huge range of options out there, and each has their pros and cons. The key advantage here is that steel seals tend to bend instead of shatter, meaning you’ll lose compression if something goes wrong, not your entire motor. Of course, not all of these aftermarket seals are created equal, and some are known to be very harsh and cause serious wear on the rotor housings over time.

For more detailed tuning information, we’ve covered our own 13B-REW build here, and once you’re through with that, you can learn everything you need to know to tune these motors here.

Get the Most From Your Mazda 13B Engine

So you’ve decided Mazda’s 13B is going to be perfect for your new build. That’s a good start, but what’s next? 

Once you’ve picked up your freshly built 13B and installed it in your vehicle, the next step is going to be a tune. 

The best move here is to start with the EFI Fundamentals and Understanding AFR (air-fuel ratio) courses, which will set you up with the foundation knowledge you need.

Once you’ve built up that foundation of knowledge, it’s time to fire up the laptop and put it all into action by checking out the Practical Standalone Tuning course. This course even has a worked example dedicated to a 13B-REW-powered RX-7 build. This means you can follow the entire tuning process from start to finish on the exact type of engine you’ll be working with.

The best part? All these courses can be bundled together at a discounted price with the Tuning Starter package

Throughout the process of learning about tuning your 13B, if you ever find yourself stuck, you’ll have access to High Performance Academy’s support forums, where you can post any questions you’ve got and get answers from tutors and the wider tuning community.

Mazda’s 13B is a unique and fascinating motor to work on, tune, modify, and drive. It’s not for everyone, but for those that properly understand and respect it, it’s more religion than motor. As far as the faithful are concerned, this high-revving, flame-popping screamer of an engine is nothing short of perfection.

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