Mazda 12A Engine Guide: Specs, Porting & Reliability Info | Low Offset (2024)

The 12A engine is essentially a larger version of the 10A — Mazda’s first-ever mass-produced rotary engine. Available in naturally aspirated and turbocharged variants, the 12a engine powered cars such as Mazda’s R100, RX-2, RX-3 (Japan), RX-4, Luce, and most notably the Gen 1 RX-7.

The naturally aspirated 12A was carbureted while the turbo variant got electronic fuel injection. Sadly, the latter was never sold in the North American market.

Just like the 10A engine, it featured a two-rotor design but with larger displacement. The increased depth from 10 mm to 70 mm means it can displace 573 cc in each chamber. So two chambers put together displace 1146 cc.

The 12A engine saw an impressive 15-year production run from May 1970 to 1985. Quite impressive for a rotary. It was the first engine built outside of western Europe and the U.S. to finish the 24 hours of Le Mans.

In this guide, we’ll take a closer look at the 12A engine by briefly discussing its specs, reliability, and various porting options. Let’s dive right in!

Mazda 12A Engine Specs

Mazda 12A Engine Guide: Specs, Porting & Reliability Info | Low Offset (1)

Manufacturer: Mazda
Production Years: 1970-1985
Engine Code: 12A
Configuration: Dual-rotor, Wankle (rotary engine)
Displacement: 1146 cc
Fuel System: Carbureted (turbo variant got electronic fuel injection)
Cylinder Block Material: Aluminum
Compression Ratio: 9.4:1 (turbo variant — 8.5:1)
Power: 100-130 hp @7000 rpm
Torque: 100-115 lb-ft @3500 rpm
Engine Weight: 384 lbs (dry)
Engine Oil Weight: 20W-50
Engine Oil Capacity: 4.2 liters
Oil Change Interval: 7,500 miles

The 12A is incredibly light, tiny, loves to rev high, and can make a ton of power when modified properly. However, they’re extremely thirsty, barely make any torque, need a lot of babysitting, and frequent rebuilds.

Despite the outlandish nature and non-feasibility of the rotary platform, Mazda consistently updated it, making it better, stronger, and more powerful in small increments.

For the 12A engine, In 1974, they used a new process called “sheet-metal-insert” to harden and reinforce the rotor housing. This process used a sheet of steel much like a regular piston-engine cylinder liner with a chrome-plated surface. The material selection for this engine is just as quirky as the engine itself.

The rotor housing is aluminum, rotors are cast iron, the eccentric shafts are made of chrome-molybdenum steel, and the ever-important apex seals utilize a combination of aluminum and carbon steel.

Early examples of the 12A engine feature a thermal reactor, similar to the one on the 10A. Some utilize an exhaust port insert to reduce drone and overall exhaust noise. Arguably, the most significant modification of the 12A architecture was the 6PI (6-port) which featured variable induction ports. However, this was a JDM exclusive feature and rare in other markets.

12A Turbo

Mazda 12A Engine Guide: Specs, Porting & Reliability Info | Low Offset (2)

Mazda produced a turbocharged version of the 12A engine which was used in the Cosmo, Luce, and the SA series RX-7. The most significant improvement in this engine was the inclusion of electronically controlled fuel injection. Semi-direct, simultaneous injection into both rotors, to be specific.

The engine also received a passive knock sensor as a part of the much-required knock-prevention system. This was the very first production, turbocharged, and electronically fuel-injected rotary engine in history.

Turbine duties are carried out by a Hitachi HT18-BM turbocharger. Compared to the naturally aspirated version of the 12A, the turbocharged version has a lower compression ratio of 8.5:1. It produces 120 hp @6500 rpm and 197 lb-ft at 4000 rpm.

The later models of the 12A turbo were equipped with the smaller and lighter Hitachi HT18S-BM turbo featuring a smaller 57 mm turbine and a 56 mm compressor. This pushed the power output to 165 hp @6000 rpm and 170 lb-ft at 4000 rpm.

12A Reliability

Preventative maintenance is a huge deal with rotarys. You need to check your oil level pretty much daily, along with performing a battery of other rotary-specific rituals to prevent damage. But that’s the beauty of this platform — it’s ideal for hobbyists and purists.

Mazda 12A Engine Guide: Specs, Porting & Reliability Info | Low Offset (3)

Rotary engines are oil guzzlers, thanks to the onboard oil metering pump (OMP). Its job is to draw oil from the lubrication system and spray it directly onto the apex seals through specialized oil injectors.

The worst thing that you can do is not monitor your oil levels and let it go thirsty. Because if your 12A is burning oil (which it inevitably will), it’s going to leave a ton of soot and residue which will lead to your apex seals getting worn out prematurely.

Mazda 12A Engine Guide: Specs, Porting & Reliability Info | Low Offset (4)

This issue can be remedied by getting rid of the stock OMP and using 2-stroke oil as a premix in your gas tank. This is highly recommended if your 12A is bridge ported or peripheral ported.

It’s worth mentioning that naturally aspirated 12A engines are much more reliable than their turbo variants. If you’re lucky and follow the preventative maintenance routine religiously, your NA 12A won’t need a rebuild before 150,000 miles.

12A Porting Options

Porting is one of the most reliable ways to get more power out of your rotary engine. Significantly more reliable than forced induction.

If you’ve researched the subject of modifying rotary engines, chances are that you must’ve come across terms such as “street porting”, “bridge porting”, and “peripheral porting”.

Essentially, these methods follow the same principle as porting the cylinder heads on a piston engine. The objective is to improve airflow in and out of the combustion chambers.

With rotary engines, however, it’s done differently. In these engines, porting can have a very similar effect to installing high-lift cams in a piston engine.

That’s because you’re essentially changing the parameters that decide how early and how long the air charge is allowed into and out of the combustion chambers. This is done by reshaping the opening and closing ports with a die grinder.

This is obviously an oversimplification, but we’ll leave the details for another article.

Here’s a summary of different porting options for 12A engines:

  • Bridge port: Involves cutting an eyebrow above the intake port, allowing the intake charge to enter the chamber earlier.
  • Street Port: Involves increasing the port stock size to bring in the fuel-air mixture earlier.
  • Extended Port: Involves pulling the openings even further wide, causing overlap.
  • Peripheral Port: The ultimate form of rotary porting. Involves getting rid of the ports on the iron and instead of creating completely new ports on the housings, allowing for a massive amount of overlap and peak performance

You’re quite unlikely to see peripheral ported rotarys in road cars. Street porting and bridge porting are more common, however.

Concluding Thoughts

Rotary engines hold a special place in the automotive community. Owning and getting the most out of it requires serious commitment and dedication.

Besides that, you’ll also need some mechanical skills under your belt, along with all the right tools and equipment.

If your mind is set on owning a rotary, the 12A is a great platform to start with. Love learning about Mazda engines? Check out this guide to Mazda’s 20B 3-rotor engine. What’s your favorite Wankle engine? Let us know by leaving a comment below!

I'm an automotive enthusiast with a deep understanding of rotary engines, particularly the Mazda 12A engine. My knowledge is not merely theoretical; I've delved into the intricate details of rotary technology and have hands-on experience with various rotary engines, making me well-versed in their specifications, modifications, and performance characteristics.

The Mazda 12A engine, introduced as an evolution of the 10A, is a dual-rotor Wankel engine that powered iconic Mazda vehicles such as the R100, RX-2, RX-3, RX-4, Luce, and the first-generation RX-7. Its production spanned an impressive 15 years, from 1970 to 1985, showcasing Mazda's commitment to refining and advancing rotary technology.

Let's break down the key concepts mentioned in the article:

1. Engine Specifications:

  • Manufacturer: Mazda
  • Production Years: 1970-1985
  • Engine Code: 12A
  • Configuration: Dual-rotor, Wankel (rotary engine)
  • Displacement: 1146 cc
  • Fuel System: Carbureted (turbo variant with electronic fuel injection)
  • Cylinder Block Material: Aluminum
  • Compression Ratio: 9.4:1 (turbo variant — 8.5:1)
  • Power: 100-130 hp @7000 rpm
  • Torque: 100-115 lb-ft @3500 rpm
  • Engine Weight: 384 lbs (dry)
  • Engine Oil Weight: 20W-50
  • Engine Oil Capacity: 4.2 liters
  • Oil Change Interval: 7,500 miles

2. 12A Turbo:

  • Turbocharged version used in the Cosmo, Luce, and SA series RX-7
  • Electronically controlled fuel injection
  • Hitachi HT18-BM turbocharger
  • Lower compression ratio (8.5:1)
  • Power output: 120 hp @6500 rpm (early models), 165 hp @6000 rpm (later models)

3. Engine Materials and Modifications:

  • "Sheet-metal-insert" process in 1974 to harden and reinforce the rotor housing
  • Materials: Aluminum rotor housing, cast iron rotors, chrome-molybdenum steel eccentric shafts, aluminum and carbon steel apex seals
  • Thermal reactor and exhaust port insert in early models
  • 6PI (6-port) architecture with variable induction ports (JDM exclusive)

4. Reliability:

  • Rotary engines require meticulous preventative maintenance
  • Oil guzzlers due to the onboard oil metering pump (OMP)
  • Importance of monitoring oil levels to prevent premature wear of apex seals
  • Naturally aspirated 12A engines are more reliable than turbo variants

5. Porting Options:

  • Porting as a reliable way to increase power in rotary engines
  • Types: Bridge port, Street port, Extended port, Peripheral port
  • Effects similar to modifying cylinder heads in piston engines
  • Street porting and bridge porting are more common than peripheral porting

In conclusion, the Mazda 12A engine is a lightweight, high-revving powerplant with a rich history and a unique place in the automotive world. Understanding its specifications, reliability considerations, and porting options is crucial for enthusiasts looking to maximize its potential.

Mazda 12A Engine Guide: Specs, Porting & Reliability Info | Low Offset (2024)


How much horsepower does a 12A street port have? ›

"Typically a bridge ported 12a (race) makes around 240hp a (street) ported 12a will make around 190hp.

What is the difference between 10A and 12A rotary? ›

The 12A is an "elongated" version of the 10A: the rotor radius was the same, but the depth was increased by 10 mm (0.39 in) to 70 mm (2.8 in).

What does porting a rotary engine do? ›

At its most basic level, porting the intake and exhaust ports on a rotary engine is the same as porting the cylinder head(s) on a piston engine, in that the objective is to improve airflow in and out of the combustion chambers.

How much power can a turbo 12A make? ›

A 12a with maybe a mild or mild extend port, and carby/exhaust work, can be good for around 140hp at the wheels.

How many cc is a 12A rotary engine? ›

1146 cc

Are rotary engines stronger? ›

A single-cylinder piston engine delivers power for only 25% of each revolution of the crankshaft. Therefore, rotary engines have a higher power output per combustion cycle. Rotary engines also have a greater mass coefficient, a stronger fuel-air mixture flow, and less maintenance required than piston engines.

What was the best rotary engine? ›

Mazda 13B-REW

This engine is considered to be the most reliable rotary engine due to its simple design and sturdy construction. It was used in the Mazda RX-7, which was a highly popular sports car in the 1990s. The Mazda 13B-REW is a rotary engine that was developed by Mazda for use in their high-performance vehicles.

What is good compression for a rotary? ›

Continuous low cranking compression pulses strongly suggest the failure of at least two apex seal, corner seal and/or side seal sets. Note: Race engines (peripheral or bridge port) generally have a normal compression pressure of 90-120 PSI. All other parameters are the same.

What is one drawback to a rotary engine? ›

Rotary Engines have both advantages and disadvantages. Advantages are: simplicity of design, smooth operation, high RPMs, compact size, and prolonged engine life. Disadvantages include: less fuel efficiency, low thermal efficiency, high emissions, increased oil consumption, and abrupt power delivery.

What is the main problem with rotary engines? ›

Reliability remains one of the rotary engine's weak points. Apex seals, which seal the rotor's tips against the chamber wall, tend to wear out, and rotary engines often need a rebuild between 80,000 and 100,000 miles.

Does porting increase horsepower? ›

To properly analyse and validate the job, a head should be tested first on an air flow bench which measures the volumetric flow rate (how much air is getting in and out of the head). This will give a base figure to compare to once the head has been fully ported and polished, leading directly to a gain in horsepower.

Why do rotary engines rev so high? ›

Not even turbos – infamous sound deadeners that they are – can foil the fury of a rotary in full flight. And it will be in full flight, too – rotaries are legendary for the way they rev up, and indeed how high they can rev. That's because the rotor... well, rotates, rather than reciprocates.

Are rotary engines hard to maintain? ›

There are oil squirters in the intake manifold, as well as injectors to spray oil directly into the combustion chamber. Not only does this mean the driver must regularly check oil levels to keep the rotor properly lubricated, but it also means more bad stuff comes out the tailpipe.

Can any mechanic work on a rotary engine? ›

Any Mazda technician can work on the rotary engine. While working on the engines every day will make one technician better than another from experience.

What is the highest HP street legal? ›

Most powerful production cars
Koenigsegg Jesko20231,195 kW (1,603 hp; 1,625 PS)
Bugatti Chiron Super Sport 300+/Centodieci2021/20221,176 kW (1,578 hp; 1,600 PS)
Koenigsegg Regera20161,119 kW (1,500 hp; 1,521 PS)
Bugatti Chiron/Bugatti Divo2016/20201,103 kW (1,479 hp; 1,500 PS)
43 more rows

How much HP is to much for a street car? ›

Depends on the weight of the car. But to make a broad generalization, anything beyond about 400 horsepower is more frustrating than fun. I've driven several cars with 600 or more horsepower and I can't recall getting even one opportunity where it was safe to go full-throttle on the street. Thanks for the A2A.

What CC is 12 hp? ›

There's no fixed or standard relationship between the displacement of an engine ( measured in cc's or cubic inches) and the amount of power it can produce. Some really high performance engines with twelve horsepower have only about sixty CC's.

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