Mazda’s 13B Rotary engine was initially launched in 1973 in the Mazda RX-4. With a lifespan of almost 40 years, the 13B is the most produced rotary engine used in production cars. With respect to the RX-7, the 13B was first used in 1984 FB GSL-SE models.
The 13B is part of Mazda’s Wankel Rotary engine line, named after Felix Wankel, the inventor of the rotary engine. Prior to the 13B variant, Mazda was using the 12A, a 1.2L twin-rotor engine produced from 1970 until 1985. The 12A powered the RX-series Mazda’s up until the FC RX-7.
The 13B has had 6 different versions throughout its longevity, 5 of which where used in RX-series cars. The 13B-REW powered the Mazda RX-7 FD, or FD3S, from 1992 until its retirement in 2002. With a twin-turbo setup, an overengineered engine, and a sporty design, the 13B REW and RX-7 FD remain highly sought after cars even to this day.
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
The early 90’s was a tuner-era for Japanese sports cars. In an effort to compete alongside German performance cars, such as BMW’s E36 M3, and American Muscle cars like Ford’s 5.0 Mustang, Japanese manufacturers were overengineering their sports cars and packing them with turbochargers to make big power in small, lightweight cars. The RX7 and Toyota’s Supra are the two best examples of this.
To compete on power with a 1.3L engine, Mazda added a sequential turbocharger system to the 13B REW. The sequential system used two turbochargers, one smaller and one larger, that operated sequentially. The first, smaller, turbo provided boost up until 4,500rpm’s when the larger turbo then kicked in to power the engine from 4,500rpms until redline.
This was the first ever mass-produced sequential turbo engine ever made. And this turbo system is a primary driver of a lot of the common engines problems the 13B REW faces due to the amount of excessive heat it produces.
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 dig into the problems themselves, it’s worth noting that Rotary engines require a lot of special attention. The 13B-REW is not a reliable engine if it is not properly taken care of. While the 13B gets a bad reputation for reliability, it is often caused by negligent owners. However with that being said, the 13B REW does have a number of common problems of its own that tend to occur regardless of maintenance.
1. 13B-REW Leaking Apex Seals
Compared to a traditional combustion engine with 40+ moving parts, the 13B REW only has three moving parts: the two rotors and the crankshaft. Rotors are shaped like rounded triangles and rotate in a circular motion inside of an oval shaped housing. Because of its triangular shape, the only parts of the rotors that touch other metal are each of its corners.
To keep compression high, the three triangle tips must keep an airtight seal in the housing. Each corner of the triangle has a seal, called an apex seal, that is pushed against the rotor housing with a spring to form the airtight connection. Apex seals are generally made of metal, and because the housing is also metal, the seals need to be lubricated with oil.
On the FD RX-7, the apex seals are one of the most common ‘engine killers’. Because the seals require constant oil, the 13B actually consumes oil in excess of traditional engines. Therefore, additional oil usually needs to be added every few months.
Both excessive heat from the engine and a lack of oil can cause the apex seals to become worn or cracked. When this happens, the seals lose their airtight connection 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
Low compression can cause a number of issues within rotary engines. The most notable symptom is going to be a big loss of power. However, if there is just a very small pressure leak, the loss of power might not be immediately noticeable.
Preventing or Repairing 13B REW Failed Apex Seals
The best way to prevent leaking apex seals is to make sure your rotary is constantly full-up with fuel. Keep an extra quart of oil in your trunk and frequently check oil levels to make sure they are not too low. The FD RX-7 tends to burn approximately 1 quart of oil for every 2,000-3,000 miles. However, consumption certainly varies by engine so I always recommend topping the 13B off every 1,000 miles just to be safe.
Unfortunately, it’s not just lack of oil that can cause the apex seals to leak. Natural wear and tear on the seals is a normal and unavoidable. On a poorly maintained 13B REW the apex seals can go bad within the 50,000-80,000 mile mark, while on a well-maintained one they can usually last from 120,000 to 150,000 miles.
If you have bad apex seals, you will need to rebuild the engine, or at least completely tear it down to replace the seals. Since they are located within the rotor housing, there is no other way to get to them. If you are replacing your seals, I would recommend using a good aftermarket/high-performance set.
2. Catalytic Converter Failure
The 13B REW uses two catalytic converters. The first cat is located within the downpipe, and the second “main” unit is located after it. Because the sequential twin-turbo system generates a lot of engine heat, the first catalytic converter is prone to burning up and clogging up the main catalytic converter.
When this happens, the exhaust air flow becomes restricted, pushing the air back into the engine and causing engine temps and exhaust gas temps (EGT’s) to skyrocket.
The most noticeable symptom of a clogged main cat is excessive EGT’s. As this causes internal engine temps to increase, it can have catastrophic damage on the engines internals and the apex seals leading to total engine failure. The best option for preventing this issue is to install a catless downpipe on your FD RX-7. While this can create issues passing emissions tests, removing the cat will improve exhaust air flow and actually lower internal engine temps which will prolong the life of your 13B.
3. Vacuum, Radiator Hoses, and Wiring Harness Failure
While the 13B REW is generally a small engine, it is also crowded into a pretty small engine bay. Because of the excess heat that the sequential turbo system produces, the temperatures within the engine bay are also very high. The excessive heat causes a number of frequent failure points across various hoses and wires located within the engine bay. Failure of these parts can cause electrical malfunction, boost leaks, engine overheating, and a number of other potentially dangerous problems.
Vacuum hoses must maintain internal pressure to function properly. The excessive engine heat can cause these hoses to harden and crack. When this happens, air can leak from the hoses, reducing pressure and causing a loss of power and overall performance. We recommend replacing all vacuum hoses with wrapped silicone hoses which can withstand much higher temperatures. The materials are super cheap but it is a rather labor intensive job, requiring 5-6 hours of work.
Radiator Hoses / Expansion Tank
The 13B’s radiator and coolant hoses, especially the ones that connect to the turbos, are also prone to warping and cracking. Additionally, there is a radiator/coolant expansion tank that is prone to failing. We recommend replacing the coolant hoses with high temperature silicon hoses. Also, there is a simple $30 modification that will completely remove the expansion tank and therefore prevent it from failing.
Again with the excessive heat, the wiring harness can also make the wiring harness brittle and prone to failure. When this happens, it will cause a number of electrical problems.
4. RX-7 FD Cracked Turbo Manifold
The 13B REW turbo manifold, or exhaust manifold, connects the turbochargers to the exhaust system and passes air out through the exhaust system. Rotary engines, like all other traditional engines, experiences heat cycles. Heat cycles are simply the heating and then cooling of engine components and occurs when you warm an engine up and them turn it off and let it cool down.
The turbo manifold is made of metal, and metal expands under heat and contracts when cold. The constant expanding and contracting in conjunction with being connected to the vibrations of the engine cause the manifold to develop cracks in the metal. These cracks can either be small hairline cracks or larger, noticeable cracks.
Small hairline cracks likely won’t cause a very noticeable performance decrease, but once a crack exists it will continue to deteriorate. Once a larger crack forms, air will begin to slip out of the cracks and therefore reduce pressure within the engine. When pressure reduces, turbochargers become less efficient and have to work harder to produce the same amounts of power. Ultimately this puts added stress on the turbos, which can cause them to fail, and will also cause 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 probably won’t be too much of a noticeable power impact. Therefore, most people will say you can continue to drive your engine normally until the cracks become bigger.
Once the cracks become large enough for a material amount of air to begin escaping, the only replacement option is the replace the manifold itself. A new manifold itself will likely run you around $1,000 and labor for replacing it will also run around $1,000 unless you are capable of DIY’ing the repair.
5. Rigorous Maintenance Requirements
While this isn’t necessarily an engine problem in itself, it does cause a lot of engine problems. These engines require proper maintenance and care. The majority of catastrophic failures with these engines are caused by owners who are not responsible or aware of the requirements of owning a rotary engine powered car.
While you should follow the recommended maintenance schedules, here are a few important items to keep in mind:
- 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 killer of these engines. There are a handful of cooling system modifications that can be made for under $100 that can drastically improve the reliability of these engines. Check out the link in the next section for a detailed list of cooling mods.
Mazda FD RX-7 & 13B REW Reliability
The 13B REW can be a reliable engine. These engines were never made to be 300,000 mile cars. They require special attention and are not the cheapest cars in the world to maintain.
On a poorly maintained engine, expect to rebuild it by the 80,000 mile mark. For meticulously maintained 13B’s, you can likely get beyond 120,000 miles before a rebuild is needed. The biggest killer of FD 13B REW engines is excessive heat. We recommend cooling system upgrades such as an aftermarket radiator, dual oil coolers, etc. Here is an awesome guide on 13B REW Cooling Upgrades.
With all that being said, these engines have a finite lifespan. Reaching the 150,000 mile mark with any major issues is possible if properly maintained. However, a majority of these engines will fail before that period, and if they do make it that far, they likely don’t have much left in them. Maintain the engine as if you want it to last forever, but understand that a complete rebuild will be a necessity at some point during the 13B REW’s life.
Upgrade the cooling system, replace the vacuum and radiator hoses, remove the downpipe catalytic converter, keep the engine well lubricated with oil, and follow the recommended maintenance schedule and the 13B REW will be bulletproof.
As far as the engine and its internals, the 13B REW can handle up to 700whp without any internal modifications necessary. The stock turbos are solid but they are generally capped at about 350whp and 15psi of boost. If you want to produce power beyond those levels, an upgraded set (or single turbo) will be required.