Mazda introduced the 13B Rotary engine in 1973 with the Mazda RX-4. The 13B is the most produced rotary engine used in production cars, with a lifespan of nearly 40 years. In terms of the RX-7, the 13B was introduced in 1984 with the FB GSL-SE models.
The 13B is a member of Mazda’s Wankel Rotary engine family, which is named after the inventor of the rotary engine, Felix Wankel. Mazda previously used the 12A, a 1.2L twin-rotor engine produced from 1970 to 1985. The 12A engine was used in Mazda’s RX-series vehicles until the FC RX-7.
The 13B has been produced in six distinct variants over the course of its existence, five of which were used in RX-series vehicles. From 1992 to 2002, the Mazda RX-7 FD, or FD3S, was powered by the 13B-REW. The 13B REW and RX-7 FD remain highly sought after cars to this day due to their twin-turbo setup, overengineered engine, and sporty design.
13B Engine Variants
- 13B AP (RX-3 and RX4)
- 13B-RESI (FB RX-7 – GSL SE models only)
- 13B-DEI (FC RX-7)
- 13B-MSP Renesis
13B REW Sequential Turbocharger System
For Japanese sports cars, the early 1990’s were a tuner era. To compete with German performance cars such as BMW’s E36 M3 and American muscle cars such as Ford’s 5.0 Mustang, Japanese manufacturers overengineered their sports cars and stuffed them with turbochargers in order to produce large amounts of power in small, lightweight vehicles. The best examples of this are the Mazda RX7 and Toyota’s Supra.
Mazda equipped the 13B REW with a sequential turbocharger system to compete on power with a 1.3L engine. Two turbochargers, one smaller and one larger, operated sequentially in the sequential system. The first, smaller turbocharger provided boost up to 4,500rpm, at which point the larger turbocharger kicked in to power the engine to redline.
This was the world’s first serial turbo engine. And this turbo system is a primary cause of a large number of the 13B REW’s common engine problems, owing to the amount of excessive heat it generates.
Mazda RX-7 13B REW Common Engine Problems
- Apex Seals & Low Engine Compression
- Catalytic Converter Failure
- Vacuum, Radiator Hoses, and Wiring Harness
- Rigorous Maintenance Requirements
- Cracked Turbo Manifolds
Before we get into the specific issues, it’s worth noting that Rotary engines require a great deal of extra care. The 13B-REW engine is not a reliable engine if not properly maintained.
While the 13B has a poor reputation for reliability, this is frequently the result of careless owners. Having said that, the 13B REW does have a number of inherent problems that tend to crop up regardless of maintenance.
1. 13B-REW Leaking Apex Seals
In comparison to a conventional combustion engine, which has over 40 moving parts, the 13B REW has only three: the two rotors and the crankshaft. The rotors are shaped like rounded triangles and rotate circularly within an oval-shaped housing. Due to the triangular shape of the rotors, the only parts that come into contact with other metal are their corners.
To maintain a high level of compression, the three triangle tips must maintain an airtight seal within the housing. Each corner of the triangle has an airtight seal called an apex seal that is pressed against the rotor housing by a spring. Apex seals are typically made of metal, and due to the metal nature of the housing, the seals must be lubricated with oil.
Apex seals are one of the most common ‘engine killers’ on the FD RX-7. Due to the constant oil consumption required by the seals, the 13B consumes more oil than conventional engines. As a result, additional oil is typically required every few months.
Both excessive engine heat and a lack of oil can result in worn or cracked apex seals. When this occurs, the seals’ airtight connection is compromised, and the engine loses compression.
Symptoms of Bad Apex Seals – 13B Rotary
- Rough idling
- Engine shuts off during idle
- Big power loss and lack of acceleration
Compression issues can manifest themselves in a variety of ways in rotary engines. The most obvious symptom will be a significant loss of power. However, if there is a minute pressure leak, the loss of power may be imperceptible.
Preventing or Repairing 13B REW Failed Apex Seals
The best way to avoid leaking apex seals is to keep your rotary engine constantly fueled. Maintain an extra quart of oil in your trunk and check your oil levels frequently to ensure they are not too low. The FD RX-7 typically consumes about 1 quart of oil every 2,000-3,000 miles.
However, because consumption varies significantly by engine, I always recommend topping off the 13B every 1,000 miles to be safe.
Regrettably, it is not only a lack of oil that can result in apex seals leaking. Natural deterioration of the seals is unavoidable. Apex seals on a poorly maintained 13B REW can fail between 50,000 and 80,000 miles, while those on a well-maintained one can typically last between 120,000 and 150,000 miles.
If your engine has failed apex seals, you will need to rebuild it or completely disassemble it to replace the seals. There is no other way to access them because they are contained within the rotor housing. If you’re replacing your seals, I’d recommend investing in a high-quality aftermarket/performance set.
2. Catalytic Converter Failure
Two catalytic converters are used in the 13B REW. The first cat is located within the downpipe, followed by the second “main” unit. Due to the high heat generated by the sequential twin-turbo system, the first catalytic converter is prone to burning out and clogging the main catalytic converter.
When this occurs, the exhaust air flow is restricted, forcing air back into the engine and increasing engine and exhaust gas temperatures (EGT’s).
Excessive EGT’s are the most noticeable symptom of a clogged main cat. As a result of the increased internal engine temperature, this can cause catastrophic damage to the engine’s internals and apex seals, resulting in engine failure.
Installing a catless downpipe on your FD RX-7 is the best way to avoid this issue. While this may cause issues with passing emissions tests, removing the cat actually improves exhaust air flow and lowers internal engine temperatures, thereby extending the life of your 13B.
3. Vacuum, Radiator Hoses, and Wiring Harness Failure
While the 13B REW is a small engine in general, it is crammed into a fairly small engine bay. Temperatures within the engine bay are also extremely high due to the excess heat generated by the sequential turbo system.
The excessive heat creates a number of frequent failure points in the engine bay’s various hoses and wires. Electrical malfunctions, boost leaks, engine overheating, and a variety of other potentially dangerous problems can result from the failure of these components.
To function properly, vacuum hoses must maintain an internal pressure. Excessive engine heat can result in the hardening and cracking of these hoses. When this occurs, air can escape the hoses, lowering the pressure and resulting in a loss of power and overall performance.
All vacuum hoses should be replaced with wrapped silicone hoses that can withstand much higher temperatures. Although the materials are inexpensive, the job is quite labor intensive, requiring 5-6 hours of work.
Radiator Hoses / Expansion Tank
Radiator and coolant hoses on the 13B, particularly those connecting to the turbos, are also prone to warping and cracking. Additionally, there is a prone-to-fail radiator/coolant expansion tank.
We recommend replacing the coolant hoses with silicon hoses that can withstand high temperatures. Additionally, there is a simple $30 modification that completely eliminates the expansion tank, preventing it from failing.
Again, excessive heat can cause the wiring harness to become brittle and prone to failure. This will result in a variety of electrical problems.
4. RX-7 FD Cracked Turbo Manifold
The 13B REW turbo manifold, also known as an exhaust manifold, connects the turbochargers to the exhaust system and directs exhaust air out. As with all other conventional engines, rotary engines undergo heat cycles.
Heat cycles are the process of heating and then cooling engine components. They occur when an engine is warmed up and then turned off and allowed to cool.
The turbo manifold is made of metal, which expands in the presence of heat and contracts in the presence of cold. The constant expanding and contracting of the manifold, combined with its connection to the engine’s vibrations, causes the metal to develop cracks. These cracks can be minute hairline fissures or larger, more noticeable fissures.
Small hairline cracks are unlikely to have a noticeable effect on performance, but once present, they will continue to deteriorate. Once a larger crack forms, air begins to escape through it, lowering the engine’s pressure.
When pressure drops, turbochargers lose efficiency and must work harder to generate the same amount of power. Ultimately, this increases the stress on the turbos, which can result in their failure and power loss.
Cracked Turbo/Exhaust Manifold Symptoms
- Low boost, lack of ability to produce boost
- Lack of acceleration, loss of power
- Exhaust smells inside of the cabin
- Whining or whistling sound from the engine
Manifold Replacement Options
If the cracks are small, there is unlikely to be a significant power impact. As a result, the majority of people will advise you to continue driving your engine normally until the cracks become larger.
Once the cracks become large enough to allow a significant amount of air to escape, the only option is to replace the manifold. A new manifold will likely cost around $1,000, and labor to replace it will likely cost around $1,000 as well, unless you are capable of performing the repair yourself.
5. Rigorous Maintenance Requirements
While this is not an engine problem in and of itself, it does contribute to a large number of engine problems. Proper maintenance and care are required for these engines. The majority of catastrophic engine failures are caused by owners who are either irresponsible or unaware of the responsibilities associated with owning a rotary engine-powered vehicle.
While you should adhere to the recommended maintenance schedules, the following are some critical points to remember:
- Add 1qt of oil every ~2,000 miles
- Change the oil and filter every 3,000 miles
- Only use non-synthetic oil
- Never shut the engine off when it’s cold
- A redline a day keeps the mechanic away (seriously, redlining it is good for the engine)
- Prevent overheating
Heat is the engine’s demise. There are a few inexpensive cooling system modifications that can significantly improve the reliability of these engines. For a comprehensive list of cooling mods, see the link in the following section.
Mazda FD RX-7 & 13B REW Reliability
The 13B REW engine is a capable performer. These engines were never intended to power cars capable of 300,000 miles. They require special care and are not the cheapest cars to maintain in the world.
Expect to rebuild an engine with poor maintenance after 80,000 miles. 13B’s that have been meticulously maintained can easily exceed 120,000 miles without requiring a rebuild.
Excessive heat is the primary enemy of FD 13B REW engines. We recommend upgrading the cooling system with an aftermarket radiator and dual oil coolers. This is an excellent guide to upgrading the cooling system on the 13B REW.
Having said that, these engines have a limited lifespan. If the vehicle is properly maintained, it is possible to reach the 150,000 mile mark without experiencing any major issues.
However, the majority of these engines will fail before that time period, and even if they do, they will likely have little left in them. Maintain the engine as if it were going to last forever, but keep in mind that a complete rebuild will be required at some point during the 13B REW’s life.
Upgrading the cooling system, replacing the vacuum and radiator hoses, removing the downpipe catalytic converter, keeping the engine well lubricated with oil, and adhering to the recommended maintenance schedule will ensure that the 13B REW is bulletproof.
In terms of the engine and its internals, the 13B REW is capable of producing up to 700whp without requiring any internal modifications. Although the stock turbos are reliable, they are typically limited to around 350whp and 15psi of boost. If you want to produce more power than that, you’ll need an upgraded set (or single turbo).