The RB25DET engine, a 2.5L turbocharged inline-six found in Nissan Skyline and Laurel models, remains a favorite among tuners seeking serious power gains. While the engine block and head can handle impressive output, the factory fuel system quickly becomes a bottleneck when you push beyond 300–350 wheel horsepower. Upgrading the fuel system with high-quality components is not just about adding raw flow—it's about delivering the right amount of fuel at the right pressure under every load condition. Nismo, Nissan's in-house performance division, offers a range of fuel system components engineered specifically for the RB platform. In this comprehensive guide, we'll explore every critical upgrade—from pump to injector to regulator—and show you how to build a fuel system that supports reliable, high-horsepower builds.

Understanding the RB25DET Fuel System

The factory RB25DET fuel system was designed for the engine's stock output of around 210–250 horsepower at the crank. It consists of a small electric fuel pump mounted inside the tank, solenoid-style injectors, a non-adjustable fuel pressure regulator, and rubber fuel lines. At pressure levels above 50 psi and flow demands exceeding the pump's capacity, the stock system can't maintain consistent rail pressure. This leads to lean air-fuel mixtures, detonation, and potential engine damage. Typical symptoms of an inadequate fuel system include hesitation under boost, rising lambda values, and a noticeable drop in power as RPM climbs. Upgrading is essential for any build targeting 400+ wheel horsepower, or for cars running larger turbochargers, ethanol-based fuels, or aggressive boost maps.

Key Upgrades for the RB25DET Fuel System

We'll break down each component upgrade, starting from the tank and moving to the rail, with specific Nismo part recommendations and installation tips.

1. High-Flow In-Tank Fuel Pump

The factory fuel pump delivers around 140–160 L/hr at the stock pressure. For medium-power builds (up to 450 hp), a drop-in upgrade like the Nismo 480 L/hr fuel pump (Nismo #A46-00-PMP1) provides ample flow while retaining the factory hanger assembly. This pump supports pressures up to 70 psi and is compatible with both gasoline and E85. For higher power levels (600+ hp), consider the Nismo 525 L/hr unit, which uses a thicker inlet screen and includes a harness pigtail for direct wiring. Installation requires removing the rear seat and access plate, then replacing the pump and pre‑filter. For best results, hardwire the pump with a relay triggered by the ECU or a Hobbs switch to ensure full voltage under boost.

2. Upgraded Fuel Injectors

Injectors are the gateway to precise fuel metering. The stock RB25DET side-feed injectors flow approximately 270–300 cc/min and reach their duty cycle limit around 350 hp. Nismo offers high-impedance side-feed injectors in 555 cc/min and 740 cc/min sizes (Nismo #A46-00-PMP3). These injectors are flow-matched and include updated O-rings and electrical connectors. When upgrading to larger injectors, you must recalibrate your ECU via a reprogrammable chip, a standalone unit, or an aftermarket piggyback system. The 555 cc/min injectors are ideal for 450–500 hp setups using pump gas, while 740 cc/min units suit E85 or high-boost applications up to 650 hp. Installation is straightforward: remove the fuel rail, swap injectors, replace the O-rings, and torque the rail bolts to specification.

3. Adjustable Fuel Pressure Regulator

A consistent fuel pressure baseline is critical for tuning accuracy. The factory regulator is non-adjustable and operates at a fixed 43.5 psi (3.0 bar) referenced to manifold vacuum. Nismo's adjustable fuel pressure regulator (Nismo #A46-00-PMP4) allows you to increase the static pressure to compensate for larger injectors or to fine-tune fuel curves. It features a 1:1 rising-rate diaphragm that maintains a constant differential pressure across the injectors, even under boost. Installing the unit involves removing the stock regulator on the end of the fuel rail, fitting the adapter base, and connecting the vacuum/boost reference line. A fuel pressure gauge is essential for setting the baseline pressure (typically 43–50 psi with the vacuum line disconnected).

4. High-Flow Fuel Lines

With increased pump flow and higher pressure, the stock 5/16" rubber fuel lines can become a restriction. Nismo offers a complete braided stainless steel line kit (Nismo #A46-00-PMP5) in -6 AN size, which supports up to 700 hp. The kit includes PTFE-lined hose, push-lock fittings, and brackets. Upgrading the lines ensures minimal pressure drop from tank to rail and eliminates the risk of rubber hose swelling or cracking under ethanol exposure. For a street-driven car, use PTFE hose for E85 compatibility; for race-only builds, nylon-braided hose can save weight.

5. High-Capacity Fuel Filter

A clean fuel supply is non-negotiable. The stock filter uses paper media and a restrictive plastic housing. Nismo's high-flow filter (Nismo #A46-00-PMP6) uses pleated stainless steel mesh with a 10-micron rating, offering superior filtration without restricting flow. It mounts in the same location as the OEM filter but uses -6 AN fittings for a direct connection to the new lines. Install it between the pump outlet and the fuel rail, ensuring the inlet/outlet direction matches the flow arrow. Replace the filter every other season or after every significant track day event.

Benefits of Nismo Components for the RB25DET

Plug-and-Play Compatibility

Nismo designs its fuel system parts to bolt directly onto the RB25DET factory hardware. Unlike universal aftermarket parts that require adapters or custom wiring, Nismo pumps use the factory hanger, injectors fit the stock rail and intake manifold, and the regulator mounts without drilling. This saves hours of fabrication time and reduces the chance of leaks.

Calibrated Performance

Every Nismo injector is flow-tested and matched within 1% of its advertised flow rate. The fuel pump curves are verified on a test rig to deliver advertised flow at the rated pressure. This consistency makes tuning easier—you can trust that the fuel map your tuner writes will translate directly to your engine.

Long-Term Durability

Nismo components are built to withstand high mileage, heat cycling, and corrosive fuels like ethanol. The injectors feature corrosion-resistant internals, the pumps use carbon commutators and sealed motor windings, and the regulator diaphragm is rated for alcohol-based fuels. This durability is essential for a daily-driven RB25DET that sees occasional track days.

Tuning and Supporting Modifications

Engine Management

Upgrading the fuel system is only half the equation. Without a tune, larger injectors and a higher fuel pressure will cause the engine to run excessively rich, leading to poor idle, black smoke, and fouled spark plugs. You must recalibrate the ECU. Popular options for the RB25DET include Nistune (a daughter-board that reprograms the factory ECU), Haltech or Link standalone ECUs, or a plug-and-play PowerFC. The tuner will set injector scaling, dead times, and the fuel pressure offset to match your hardware.

Wideband O2 Sensor

Install a wideband air-fuel ratio gauge and sensor in the downpipe. A target lambda of 0.78–0.80 at wide-open throttle (around 11.5:1 on gasoline) is safe for pump gas; with E85, target 0.85–0.88 lambda. Monitor the gauge during your first pulls to verify the fuel system holds pressure and the injectors are delivering the correct pulse width.

Return-Line Configuration

If you're using the Nismo adjustable regulator, decide whether to run a return-style or returnless system. On the RB25DET, a return-style system (where excess fuel flows back to the tank) is easier to tune and more forgiving. Simply connect the regulator's return port to a -6 AN line back to the tank. This configuration maintains stable rail pressure regardless of pump speed.

Step-by-Step Installation Overview

  1. Disconnect battery negative terminal and relieve fuel pressure by pulling the pump relay and cranking the engine.
  2. Remove rear seat and access plate to reach the fuel pump. Disconnect hoses and electrical plug, then pull the pump hanger.
  3. Install the Nismo pump onto the hanger, using the supplied gasket and filter sock. Reinstall the hanger and reconnect the wiring.
  4. Upgrade fuel lines from the pump outlet to the engine bay. Remove the old rubber lines and run the -6 AN PTFE hose, securing with clamps.
  5. Replace the fuel filter by disconnecting the old unit and installing the Nismo filter with new fittings.
  6. Swap injectors: remove the fuel rail, extract old injectors, lubricate new O-rings with clean engine oil, press injectors into the rail and manifold. Torque rail bolts to 12–15 ft-lbs.
  7. Install the adjustable regulator on the rail end. Connect vacuum line to a manifold port. Set static pressure to desired value (e.g., 43 psi for 555 cc injectors on pump gas).
  8. Prime the system by cycling the ignition (without starting) several times to build pressure. Check for leaks at every fitting.
  9. Start the engine and let it idle. Adjust the pressure if necessary and confirm no fuel odor. Then load the base tune.

Conclusion

Building a reliable, high-horsepower RB25DET starts with a properly sized fuel system. Nismo's dedicated components offer a matched set of upgrades that work together seamlessly—from the pump to the injectors to the regulator. By following the upgrade path outlined here, you can confidently push your engine beyond 500 horsepower while maintaining safe air-fuel ratios and long component life. Don't stop at just the pump and injectors; include the lines, filter, and adjustable regulator to eliminate every weak link. Combine these hardware upgrades with a professional ECU tune, and your RB25DET will deliver the power you've been chasing with the reliability that Nismo engineering guarantees.