The Definitive Guide to Mazda RX7 Engines: 12A and 13B Rotary Powerhouses

The Mazda RX7 is a legendary sports car known for its unique and high-revving rotary engines. Throughout the RX7’s production history, two rotary engines have stood out as the most iconic and widely used: the 12A and 13B. In this comprehensive guide, we’ll dive deep into the technical specifications, performance characteristics, and key differences between these two remarkable powerplants.

The 12A Rotary Engine

The 12A engine was the first rotary power plant to grace the Mazda RX7, found in the model’s initial generation produced from 1978 to 1985. This 1.2-liter, twin-rotor design was a marvel of engineering, delivering impressive performance for its time.

Technical Specifications

  • Displacement: 1,146 cc (69.9 cu in)
  • Rotor Dimensions: 85 mm (3.35 in) x 80 mm (3.15 in)
  • Compression Ratio: 9.4:1
  • Horsepower: 100-135 hp, depending on model and year
  • Redline: Approximately 7,000 RPM

The 12A engine was naturally aspirated, meaning it relied solely on atmospheric pressure to draw in the air-fuel mixture. This design, while not as powerful as the later turbocharged variants, offered a linear and responsive power delivery that many enthusiasts still cherish today.

The 13B Rotary Engine

which engine rx7

The 13B engine was the powerhouse that propelled the second and third generations of the Mazda RX7, produced from 1986 to 2002. This 1.3-liter, twin-rotor design represented a significant evolution in rotary technology, offering increased displacement and the option of forced induction.

Technical Specifications

  • Displacement: 1,308 cc (79.8 cu in)
  • Rotor Dimensions: 86 mm (3.39 in) x 86 mm (3.39 in)
  • Compression Ratio: 9.0:1 (naturally aspirated), 8.5:1 (turbocharged)
  • Horsepower: 160-280 hp, depending on model and configuration
  • Redline: Approximately 7,000 RPM (naturally aspirated), 8,000 RPM (turbocharged)

The 13B engine was available in both naturally aspirated and turbocharged variants, allowing for a wide range of performance capabilities. The naturally aspirated version produced around 160 horsepower, while the turbocharged model could output an impressive 280 horsepower, making it a formidable force on the road and track.

Key Differences

While the 12A and 13B rotary engines share a common design philosophy, there are several notable differences between the two:

Specification 12A 13B
Displacement 1.2 liters 1.3 liters
Rotor Dimensions 85 mm x 80 mm 86 mm x 86 mm
Compression Ratio 9.4:1 9.0:1 (NA), 8.5:1 (Turbo)
Horsepower 100-135 hp 160-280 hp
Redline ~7,000 RPM ~7,000 RPM (NA), ~8,000 RPM (Turbo)
Forced Induction None Turbocharged option available

The increased displacement and the availability of turbocharging in the 13B engine allowed for a significant boost in power output compared to the 12A. This made the 13B-powered RX7s more potent performers, particularly in the later turbocharged models.

Swapping Engines in the Mazda RX7

Replacing the rotary engine in an RX7 with a different type of engine, such as an LS3 V8, is a complex and challenging task that requires extensive modifications. This process involves significant changes to the chassis, drivetrain, and wiring systems, as well as the fabrication of custom engine mounts and other components.

It is a task best left to experienced mechanics and fabricators, as the level of expertise and specialized knowledge required can be daunting for the average DIY enthusiast. Attempting such a swap without the proper skills and resources can lead to costly mistakes and potentially compromise the vehicle’s safety and performance.

Conclusion

The Mazda RX7’s rotary engines, the 12A and 13B, have become legendary in the automotive world for their unique design, high-revving nature, and impressive performance capabilities. Understanding the technical specifications and key differences between these two powerplants is crucial for any RX7 enthusiast or owner looking to maintain, modify, or restore their beloved sports car.

Whether you’re a seasoned RX7 owner or simply a fan of rotary engines, this guide has provided you with a comprehensive overview of the 12A and 13B rotary engines, equipping you with the knowledge to fully appreciate the engineering marvels that have defined the Mazda RX7 legacy.

References

  1. RX7Club.com – Differences between RX8 and RX7 Engine
  2. CarGurus – Mazda RX7 Rotary engine??
  3. RX7Club.com – How is displacement measured?