The Subaru BRZ & the Need for More Fuel

The Subaru BRZ, along with its Toyota 86 and Scion FR-S siblings, has earned a cult following for its near-perfect 50:50 weight distribution, low center of gravity, and razor-sharp handling. The FA20 engine, while peppy and responsive from the factory, leaves a significant amount of untapped potential on the table. Many owners quickly discover that the stock fueling system becomes a bottleneck as soon as you move beyond basic bolt-ons like a cat-back exhaust or an intake. If you are planning to run forced induction, switch to E85, or even just optimize a naturally aspirated build with aggressive cams and a header, the factory injectors will max out before you reach meaningful power. This is where the upgrade to Siemens Deka 750cc fuel injectors becomes a logical, cost-effective solution.

While you will often see claims online of a simple injector swap adding 60 horsepower, the truth is that injectors themselves do not make power. They provide the fuel flow needed for the engine to safely consume more air and fuel, especially after tuning. The 60 HP figure is realistic when the injectors are paired with other modifications like a turbocharger, supercharger, or E85 conversion, combined with a professional tune. This article will walk through everything you need to know about upgrading to Siemens Deka 750cc injectors on your Subaru BRZ, from the technical specifications and expected power gains to installation tips and tuning requirements.

Stock Injector Limitations

The FA20 engine in the BRZ ships with fuel injectors rated at approximately 200cc per minute at the factory. For a normally aspirated engine running pump gas, these injectors provide adequate fuel for about 200 horsepower at the wheels. However, as soon as you begin to increase airflow through porting, cams, headers, or especially forced induction, the duty cycle of these stock injectors quickly climbs past the safe 80% threshold. Once an injector exceeds 80% duty cycle, fuel delivery becomes inconsistent, and you risk running the engine lean under high load – a recipe for detonation and catastrophic engine failure.

Even if you are staying naturally aspirated but plan to run E85, the stock injectors are insufficient. E85 requires roughly 30% more fuel volume than gasoline to achieve the same air-fuel ratio. That means a stock BRZ injector, already near its limit on gasoline, cannot deliver enough fuel on E85 for any significant power increase. Upgrading to a 750cc injector provides nearly four times the flow capacity, giving you massive headroom for both pump gas and alcohol-based fuels.

Siemens Deka 750cc Injectors: Specifications & Benefits

Siemens Deka injectors, often branded as Bosch EV14 or Lucas/Deka, are among the most popular high-performance injectors in the aftermarket. The 750cc rating refers to the flow rate at 43.5 psi (3 bar) of fuel pressure – a common reference point. These injectors are pintle-type, meaning they use a small disc with holes to atomize the fuel, offering excellent spray pattern and consistency.

Key specifications:

  • Flow Rate: 750cc/min at 3 bar (approximately 72 lb/hr).
  • Impedance: Low impedance (approximately 3.0 ohms). Most FA20 standalone ECUs and many piggyback controllers require a low-impedance injector driver, though some will work with resistors.
  • Body Length: Standard high-impedance-style body size, but with a low-impedance coil design.
  • Spray Pattern: Multi-hole disc (typically 4 or 6 holes) for fine atomization.

Why choose these over other brands or sizes?

  • Reliability: Siemens Deka injectors are built with hardened steel internals and high-quality seals, capable of handling high fuel pressure and aggressive ethanol blends without corrosion or sticking.
  • Tuning Support: Most aftermarket ECUs from Haltech, Link, MoTeC, AEM, and even open-source tunes via BrzEdit or ECUTek have well-documented latency and flow data for these injectors, making calibration straightforward.
  • Scalability: 750cc is a sweet spot for the FA20. It supports up to around 450-500 wheel horsepower on pump gas, and about 350-400 on E85, depending on boost level and fuel pressure. This covers the vast majority of street and track builds without going to an oversized injector that compromises idle quality.

Comparing to Other Options

Many owners consider injectors from FIC (Fuel Injector Clinic), Injector Dynamics, or even Denso. The Siemens Deka 750cc injectors are often more affordable than the ID series while offering similar performance. They also tend to idle better than older, larger Bosch or Lucas injectors because of the modern EV14-style design. For the BRZ, the commonly used adapter kit from companies like Radium Engineering or IAG Performance adds a simple clip-on harness to adapt the factory connector to the Siemens Deka pins, making installation a direct swap.

Realistic Power Gains: The 60 HP Explanation

The claim of a 60 horsepower increase from upgrading injectors is often misunderstood. The injectors themselves do not create power; they enable the engine to safely operate at higher power levels by delivering the necessary fuel. Any horsepower gain from an injector swap alone on a stock engine would be negligible, perhaps 1-2 HP from slightly improved atomization at high RPM. The 60 HP figure comes from a specific recipe:

  1. Forced Induction: Adding a turbocharger (e.g., a Garrett GT2871 or a Rotrex supercharger) dramatically increases airflow. The stock injectors will run out of fuel at around 6-8 psi, while the 750cc injectors allow safe operation up to 12-15 psi on pump gas. With proper tuning and intercooling, a BRZ on a mild turbo setup can easily see a 60 HP gain over a stock engine by going from 200 whp to 260+ whp.
  2. E85 Fuel: Running E85 can yield an additional 10-15% power increase over pump gas due to its higher octane and cooling effect. However, the stock injectors cannot deliver enough volume. Installing 750cc injectors and a retune for E85, without changing anything else, can free up 10-15 HP from leaner, cooler mixtures. Combined with a tune for ignition advance, total gains can be 20-30 HP.
  3. Header & Tune: A common first step for NA owners is a catless unequal length or equal length header plus a tune. With the stock injectors, you might gain 15-20 HP. With 750cc injectors and a tune optimized for top-end fueling, you might squeeze an additional 5-10 HP because you can run a richer mixture at high RPM for more consistent combustion.

So the "60 HP gain" is not from the injectors alone but from the combined effect of injectors + forced induction or E85 + tune. It is a safe and realistic expectation if you are building a car with those goals. For a naturally aspirated BRZ with only bolt-ons, a more typical gain from a full injector upgrade plus tune is 20-30 HP.

Supporting Modifications You Must Consider

An injector upgrade is not a standalone modification. To safely and effectively use the increased fuel flow, you will likely need:

  • Upgraded Fuel Pump: The stock fuel pump may struggle to maintain pressure at high flow demands, especially on E85. A popular option is the DW200 or AEM 340 lph pump. This ensures you don't starve the injectors at high boost.
  • Fuel Pressure Regulator (FPR): If you are running a return-style fuel system, an adjustable FPR allows you to set base pressure precisely, which is critical for injector flow calibration. Many BRZ builds retain the factory returnless system with a higher-flow pump and rely on the ECU to compensate, but an FPR gives more control.
  • ECU Tune: This is non-negotiable. The factory ECU (ECUtek or RomRaider/BrzEdit) or a standalone ECU must be recalibrated for the larger injectors. You will need to change injector scaling, latency, and the fuel map. Without a tune, the engine will run extremely rich and may stall or foul spark plugs.
  • Injector Adapter Harness: Siemens Deka injectors have a different electrical connector than the factory Subaru injectors. You will need a set of pigtail adapters (about $20-$40) or a harness from a company like Injector Dynamics or Radium Engineering.
  • Intake and Exhaust Upgrades: To take advantage of increased fuel flow, the engine must also be able to move more air. A high-flow intake and a quality header with a full exhaust system will help realize the power gains from the injectors.

Installation Guide: Step-by-Step

Installing injectors on a BRZ is a moderate DIY job for those with mechanical skills. Expect to spend 2-4 hours. Always work with a cool engine and disconnect the battery negative terminal.

Tools and Parts Needed

  • Siemens Deka 750cc injectors (set of 4)
  • Injector adapter harness (if needed)
  • Fuel line disconnect tool (for Subaru quick-disconnect fittings)
  • 10mm and 12mm sockets, ratchet, extensions
  • Torx bits (for intake manifold if needed)
  • Shop towels, safety glasses, fire extinguisher
  • New injector o-rings (usually included with injectors)

Procedure

1. Depressurize the fuel system. Remove the fuel pump fuse, start the engine, and let it stall. Then crank for a few seconds to relieve residual pressure. Disconnect the negative battery cable.

2. Remove the intake manifold. On the BRZ, the fuel rail sits underneath the intake manifold. You will need to unbolt the manifold from the heads (about 8 bolts) and lift it off. Label any vacuum lines or sensors. You do not need to completely remove the wiring harness; just carefully move it aside.

3. Disconnect the fuel lines. Use the quick-disconnect tool to release the fuel supply line from the rail. Have a towel ready, as some fuel may still drip.

4. Remove the fuel rail. Unbolt the rail from the cylinder heads (M6 bolts). Carefully lift the rail with the injectors still attached. Remove the old injectors by pulling them out of the rail and intake manifold ports. Slide old o-rings off.

5. Install the new injectors. Lubricate the new o-rings with a small amount of clean engine oil or Vaseline to prevent tearing. Install the injectors into the fuel rail first, ensuring they fully seat. Then press the rail and injectors into the intake manifold ports. Tighten the rail bolts to factory torque (around 8 ft-lbs). Do not overtighten.

6. Connect the electrical adapters. Attach the adapter harness to each injector and then to the factory wiring. Ensure the clips click.

7. Reconnect fuel lines and reassemble. Attach the fuel supply line (you should hear a click). Reinstall the intake manifold with a new gasket if needed. Torque the manifold bolts in a cross pattern to 14 ft-lbs. Reconnect vacuum lines, sensors, and the battery.

8. Check for leaks. Turn the key to the ON position (do not start) to pressurize the fuel system. Inspect all injector seals and connections for leaks. If none, start the engine and check again. If there is a misfire, you may have a bad injector or incorrect electrical connection.

Tuning the ECU for the New Injectors

After installation, you must reprogram the ECU. If you are using ECUTek with a professional tuner, they will adjust the injector scaling factor (the size of the injector relative to the stock). The latency (dead time) table must also be updated, as low-impedance injectors open and close faster than stock high-impedance injectors. A typical starting point for Siemens Deka 750cc injectors on an FA20 is an injector scaling of 750/200 = 3.75, but this will need fine-tuning based on actual fuel pressure and voltage.

If you are using a standalone ECU (e.g., Haltech Elite 1500), the injector setup is more straightforward because you can input the injector flow data directly. Many tuners have specific base maps for BRZ builds with these injectors. It is highly recommended to have the car professionally tuned on a dyno to ensure safe air-fuel ratios and optimal ignition timing.

Caution: Do not attempt to drive the car more than a few miles without a tune. The engine will run overly rich, which can foul spark plugs, dilute oil, and damage the catalytic converter. In extreme cases, unburned fuel can cause backfires or even damage the O2 sensors.

Common Pitfalls and How to Avoid Them

  • Wrong injector impedance: Ensure you are using low-impedance (3.0 ohm) versions. Some aftermarket injectors marketed as "high impedance" are actually standard injectors. Siemens Deka 750cc are low-impedance; your ECU must support that or use a resistor pack.
  • Incorrect fuel pump: The stock pump may not keep up at high flow. Upgrade the pump before tuning, especially on E85. A failing pump at high loads can cause a lean misfire and engine damage.
  • Leaking o-rings: Always lubricate o-rings and replace them if they came used. Even a small vacuum leak at the injector seat can cause a lean condition or fuel odor.
  • Skipping the tune: This is the most common mistake. Do not install injectors and immediately drive hard. Get a base map from your tuner or use a preloaded file from a reputable source.

External Resources & Further Reading

For more detailed technical information and community experiences, check these resources:

  • Innovate Motorsports – Offers wideband controllers essential for tuning.
  • Delphi Technologies – Parent company of Siemens Deka injectors; technical data sheets available.
  • FT86Club Forum – Extensive user reviews and installation guides for injector swaps on the BRZ platform.
  • Radium Engineering – Adapter harnesses and fuel system components for the BRZ.

Conclusion

Upgrading to Siemens Deka 750cc injectors on your Subaru BRZ is a well-proven path to significantly higher horsepower, especially when combined with forced induction or E85. The 60 HP number is achievable when the injectors are part of a complete system: proper fuel delivery, engine breathing, and a professional tune. The installation itself is within the reach of a skilled DIYer, but the tuning should be left to a professional to ensure reliability and safety. With the right supporting modifications, these injectors transform the FA20 from a fun daily driver into a formidable track weapon or street machine. Always plan your build carefully, and enjoy the process of unlocking your BRZ’s true potential.