Maximizing Power Gains on the Mazda FD RX-7: Top Turbo Upgrades from HKS and Greddy

The Mazda FD RX-7 remains a benchmark in the sports car world, celebrated for its lightweight chassis, near-perfect weight distribution, and the distinctive 13B-REW twin-rotor engine. However, even in its factory twin-turbo form, the FD’s power potential is limited by conservative boost levels and aging turbocharger technology. Enthusiasts who want to truly unlock the rotary’s high-revving character and immense horsepower ceiling turn to aftermarket turbo upgrades. Among the most respected names in forced induction for the RX-7 are HKS and Greddy (Trust).

In this guide, we will explore the top turbo upgrade options from both manufacturers, explain why each kit suits different power goals, and outline the supporting modifications necessary to make big boost both reliable and drivable. Whether you are building a street-driven weekend warrior or a dedicated track machine, understanding the nuances of these turbo systems is essential for maximizing power gains without compromising the soul of the rotary.

Understanding the Rotary Engine and Its Turbocharging Needs

The 13B-REW rotary engine is fundamentally different from a piston engine. It uses a triangular rotor that orbits within a housing, creating three combustion chambers per revolution. This design gives the rotary a high power-to-weight ratio, exceptionally smooth operation, and the ability to rev well past 8,000 RPM with the right supporting mods. However, the rotary also presents unique challenges for turbocharging.

  • Exhaust gas temperature (EGT) — Rotaries run hotter than piston engines, especially under boost. Excessive EGT can destroy apex seals and housings. Turbo upgrades must be paired with efficient wastegating and proper timing.
  • Airflow characteristics — The rotary’s continuous combustion cycle creates a distinct exhaust pulse pattern. Turbos that work well on piston engines may surge or lag on a rotary. Companies like HKS and Greddy design their turbine housings and wheel trims specifically for the 13B’s pulse profile.
  • Compression ratio — Factory rotors have a low compression ratio (~9.0:1) to handle boost. Aftermarket turbos allow higher boost levels but require upgraded fuel systems and intercooling to prevent detonation (which is catastrophic on a rotary).

Given these factors, bolting on any large turbo is not enough. The entire intake, exhaust, fueling, and engine management system must be synchronized. HKS and Greddy have decades of experience with the 13B-REW, and their complete turbo kits are engineered to address these specific challenges while delivering significant power gains.

Benefits of Upgrading the Turbocharger

While the stock sequential twin-turbo system on the FD RX-7 (producing around 255–276 hp depending on market) provides acceptable performance for its era, it has well-known limitations: complex vacuum lines, prone to boost creep, and difficult to maintain high power levels. Aftermarket single-turbo upgrades from HKS and Greddy offer several advantages:

  • Substantial horsepower gains — Many kits push the 13B-REW into the 350–500 whp range with modest boost, and even higher with proper fueling and tuning. Rotaries respond extremely well to increased airflow due to their free-breathing design.
  • Improved throttle response and spool — By eliminating the complicated sequential system and using a single, properly sized turbocharger, you gain immediate throttle response and predictable power delivery.
  • Greater reliability — Aftermarket turbochargers from HKS and Greddy feature modern journal or ball-bearing cartridges, improved oil and water cooling, and stronger turbine wheels that can withstand sustained high boost without failure.
  • Simplified engine bay — Removing the twin-turbo plumbing cleans up the engine bay, reduces weight, and makes maintenance easier.
  • Higher ceiling for future modifications — Once the turbo system is upgraded, you have a solid foundation for further power increases with porting, larger injectors, alcohol injection, or even a standalone ECU.

Top Turbo Upgrades from HKS

HKS is a Japanese tuning icon, and their FD RX-7 turbo kits have been tested on countless builds worldwide. They offer a range of turbo upgrades tailored to different power goals, from street-friendly options to race-only monsters.

HKS GT2835 Turbo Kit

The HKS GT2835 is one of the most popular single-turbo upgrades for the FD RX-7. It strikes an excellent balance between quick spool and high peak power, making it ideal for street-driven cars that occasionally see track time.

  • Specifications: The GT2835 features a 52-trim compressor wheel and a 60-trim turbine wheel in a T25 footprint, with a 0.64 or 0.86 A/R turbine housing option. The ball-bearing center section ensures low friction and rapid spool-up.
  • Power output: With proper tuning and supporting mods (fuel pump, injectors, intercooler), the GT2835 can produce between 350 and 420 whp on pump gas. On race fuel or E85, numbers above 450 whp are possible.
  • Spool characteristics: Full boost (around 12–15 psi) arrives by 3,200–3,500 RPM on a street port engine, giving the RX-7 a broad, torquey powerband that pulls hard to redline. This makes the GT2835 one of the most responsive single-turbo options for the 13B-REW.
  • Included components: HKS provides a cast-iron exhaust manifold (often with an integrated wastegate port), downpipe, oil and water lines, and all necessary gaskets. The kit is designed as a bolt-on solution with minimal fabrication required.
  • Best for: Enthusiasts who want a fast-spooling, reliable upgrade that transforms the FD into a quick street car without sacrificing daily drivability. It is also a great foundation for a 12A or 13B street port engine.

View the HKS GT2835 product page

HKS GT-RS Turbo (GT-RS II)

For those who want extreme performance and are willing to trade some low-end spool for top-end power, the HKS GT-RS (now GT-RS II) turbo is a formidable choice. This turbo is based on the Garrett GT30/GT35 platform and is engineered for high boost levels and sustained high-RPM power.

  • Specifications: The GT-RS uses a 56-trim or larger compressor wheel and a 76-trim turbine wheel with a T3 or T4 flange. The turbine housing is typically a 0.84 or 1.06 A/R, optimized for rotary exhaust pulses. The GT-RS II version has an improved bearing system for even faster spool.
  • Power output: On a built rotary with race fuel, the GT-RS can push beyond 600 whp. More conservative builds with pump gas and moderate boost (18–20 psi) typically land in the 450–520 whp range.
  • Spool characteristics: Because of the larger turbine and compressor, full boost comes on later, around 4,000–4,500 RPM. However, once it spools, the power delivery is relentless, with the engine continuing to pull hard past 8,000 RPM. This turbo rewards aggressive driving on the track.
  • Installation notes: The GT-RS is a larger unit, so it may require modifications to the engine bay, such as relocating the battery or trimming the fan shroud. HKS supplies a heavy-duty manifold and downpipe, but you may need custom intake piping to match the larger compressor outlet.
  • Best for: Serious power hunters who plan to build their engine internals and use the RX-7 primarily for track days, drag racing, or high-horsepower street pulls. It pairs well with a large street port or bridge port engine.

Explore the HKS GT-RS series

Top Turbo Upgrades from Greddy (Trust)

Greddy, known in Japan as Trust, offers another lineage of proven turbo kits for the FD RX-7. Their kits are known for robust construction, thoughtful engineering, and compatibility with many aftermarket ECU systems.

Greddy TD06SH Turbo Kit

The Greddy TD06SH is a legendary single-turbo upgrade that has been powering fast RX-7s for decades. The “SH” stands for “Super High-output,” and this turbo is designed to deliver serious power while maintaining a reasonable boost threshold for street use.

  • Specifications: The TD06SH uses a 20G or 25G compressor wheel (depending on the specific trim) and a 10cm² or 12cm² turbine housing. The TD06 turbine is a proven size that flows well on the 13B-REW without excessive lag. Greddy typically includes an oil-cooled center section.
  • Power output: With supporting modifications, the TD06SH can produce 400–500 whp on pump gas and well over 550 whp with higher boost and race fuel. It thrives in the 450–480 whp range, where it offers excellent drivability and a broad powerband.
  • Spool characteristics: The TD06SH spools slightly later than the HKS GT2835 but earlier than the GT-RS. Expect full boost by around 3,600–4,000 RPM. This makes it a great all-rounder: punchy enough for street pulls but with enough top-end to satisfy track enthusiasts.
  • Kit contents: Greddy provides a cast iron exhaust manifold (known for durability), a stainless steel downpipe, oil drain tube, and all necessary gaskets. Many kits also include a blow-off valve adapter and a boost control solenoid.
  • Best for: Builders who want a proven, no-nonsense turbo setup that can handle aggressive driving without constant maintenance. It is a popular choice for street ported engines and is compatible with most aftermarket intercooler piping kits.

Check the Greddy TD06SH kit details

Greddy T518Z Turbo

The Greddy T518Z is a smaller, more responsive turbo that appeals to owners who prioritize immediate throttle response and low-end torque over peak horsepower numbers. It is derived from the T51R design but optimized for quicker spool.

  • Specifications: The T518Z features a 52-trim compressor wheel and a 59-trim turbine wheel with a 0.64 A/R turbine housing. Journal bearings keep the cost down, but the wheel trim is carefully chosen to match the 13B’s flow requirements.
  • Power output: This turbo is happiest producing 300–380 whp on pump gas. It is not intended for extreme power levels but delivers a strong, linear curve that feels much faster than the stock twin-turbo setup.
  • Spool characteristics: Full boost can be achieved as early as 2,800–3,200 RPM, depending on engine porting and exhaust setup. This makes the T518Z a joy to drive on the street—boost builds almost instantly, and the car responds eagerly to throttle inputs.
  • Installation ease: Like most Greddy kits, the T518Z includes a cast manifold and downpipe designed for a direct bolt-on fit. It is one of the simplest single-turbo conversions available for the FD RX-7.
  • Best for: Daily drivers or enthusiasts who want a substantial upgrade from stock without the cost or complexity of a large turbo. It pairs perfectly with a mild street port and a good ECU tune. For those who autocross or drive twisty roads, the T518Z provides instant power out of corners.

See the Greddy T518Z kit

Installation Considerations and Supporting Modifications

A turbo upgrade is not a standalone modification. To fully realize the potential of any HKS or Greddy kit, you must address the supporting systems. Here are critical considerations for a successful installation:

Fuel System Upgrades

High boost requires more fuel. The stock FD fuel pump and injectors are insufficient for most turbo upgrades. Minimum requirements:

  • Larger fuel pump (e.g., Walbro 255 lph or Aeromotive 340 lph)
  • Upgraded injectors: 550–750 cc/min for moderate builds, 1,000+ cc/min for high-power setups. Primary and secondary injectors must be properly matched.
  • Adjustable fuel pressure regulator and larger fuel lines if pushing beyond 450 whp.

Intercooling and Intake

Rotaries generate high intake air temperatures under boost. A front-mount intercooler (FMIC) is strongly recommended. Most HKS and Greddy kits assume you have or will purchase a separate FMIC kit. Also consider a larger air filter and smooth intake piping to reduce restriction.

Engine Management and Tuning

The stock ECU cannot handle the airflow of a large single turbo. You will need:

  • A piggyback system (e.g., Power FC) or a standalone ECU (Haltech, MoTeC, AEM).
  • Professional tuning on a dyno. Rotary engines are sensitive to lean conditions and detonation. Improper tuning can destroy the engine quickly.
  • Wideband oxygen sensor and boost gauge for monitoring.

Exhaust System

Downpipe and exhaust must be upgraded to match the turbo outlet. 3-inch mandrel-bent systems are standard for most single-turbo FD builds. A free-flowing catalytic converter (or test pipe) and cat-back exhaust will reduce backpressure and improve spool.

Cooling and Oil System

Increased power generates more heat. Consider:

  • High-capacity radiator (Koyo, Fluidyne) and oil cooler.
  • Oil restrictor for the turbo feed line to prevent over-oiling.
  • Upgraded thermostat and possibly an electric fan setup for street cars in hot climates.

Professional Installation vs. DIY

While many FD owners are mechanically adept, a turbo conversion involves welding, custom fabrication for downpipes, and precise alignment of turbo flange to manifold. Unless you have experience, professional installation is recommended. HKS and Greddy kits are “bolt-on” in the sense that they include most hardware, but you may still need to fabricate intercooler piping or relocate components.

Tuning and Maintenance for Longevity

Once the turbo upgrade is installed and tuned, ongoing maintenance becomes even more critical for a rotary engine. Here are tips to keep your built FD reliable:

  • Use high-quality synthetic oil and change it every 2,000–3,000 miles. Rotary engines consume oil by design, and turbo heat can break down oil quickly.
  • Allow the engine to cool down before shutting off after a hard drive. An aftermarket turbo timer is a wise investment.
  • Monitor boost pressure and air-fuel ratio consistently. Any deviation from tune could indicate a problem.
  • Inspect the turbo regularly for shaft play or oil leaks.
  • Consider upgrading to a larger wastegate if you experience boost creep or poor boost control.

Conclusion

Upgrading the turbocharger on your Mazda FD RX-7 is the most effective way to unlock the rotary engine’s true potential. HKS and Greddy offer a range of solutions tailored to different driving styles and power targets. The HKS GT2835 and Greddy T518Z are ideal for street-focused builds that prioritize quick spool and drivability, while the HKS GT-RS and Greddy TD06SH cater to those seeking higher horsepower numbers for track or competitive use.

No matter which turbo you choose, remember that supporting modifications—fuel system, intercooling, engine management, and proper tuning—are non-negotiable for reliability. A well-executed turbo upgrade transforms the FD RX-7 from a legendary sports car into a genuinely fast machine that can hold its own against modern performance cars. Plan your build carefully, choose the turbo that matches your goals, and enjoy the rotary experience at its most exhilarating.

For more information on specific kits and technical specifications, visit the official HKS and Greddy websites, or consult with a reputable rotary shop like Rotary Aviation or Pineapple Racing for application-specific advice.