Table of Contents
The R33 GT-R Fuel System: From Factory to 500+ HP
The Nissan Skyline R33 GT-R is a legendary machine, but its factory fuel system was designed for 276 horsepower (Japanese gentleman's agreement) and stock boost levels. To reliably support 500+ wheel horsepower, every component from the tank to the injector tip must be upgraded. This guide covers the critical fuel system modifications—starting with Walbro fuel pumps and properly sized injectors—backed by the supporting hardware and tuning required to keep your RB26DETT healthy at high power levels.
Why the Stock Fuel System Falls Short Above 500 HP
At 500+ whp, the stock fuel pump cannot maintain adequate pressure and flow. The OEM pump is a single in-tank unit that struggles above approximately 400 flywheel horsepower. The injectors (typically 370cc on early R33 models) are maxed out well before 500 HP. The fuel pressure regulator and hard lines also introduce restrictions. Running lean under boost is the fastest way to destroy an engine—proper fuel system planning is non-negotiable.
Reputable JDM suppliers and community forums like SAU provide real-world data on these limits.
Walbro Fuel Pump Options for the R33 GT-R
Walbro has been a trusted name in high-flow fuel pumps for decades. For an R33 GT-R targeting 500–700 whp, the most common choices are the Walbro 255 lph (GSS342) and the Walbro 450 lph (F90000285) high-flow pumps.
Walbro 255 lph (GSS342)
- Flow capacity: Supports up to approximately 600 whp on gasoline when used with a single pump setup and proper wiring.
- Fitment: Drops directly into the R33 GT-R factory hanger with the included kit—no major modifications needed.
- Limitation: At higher boost levels (over 25 psi) the 255 lph may not maintain adequate amp draw. A dedicated 12-volt relay and heavy-gauge wiring are essential.
Walbro 450 lph (F90000285)
- Flow capacity: Capable of supporting up to 900 whp when used in a single pump configuration with aftermarket hardwire. Also works well as a primary pump in a dual-pump setup for extreme builds.
- Size: Slightly larger than the 255—may require minor trimming of the factory hanger or the use of an aftermarket fuel pump bucket.
- Noise: The 450 lph pump is noticeably louder than the 255, though this is seldom a concern in a performance-oriented car.
Installation Best Practices
Regardless of which Walbro pump you choose, proper installation is critical. Always replace the fuel pump strainer with a high-flow unit. Use a relay trigger from the ECU or a boost switch so the pump runs on a dedicated power feed. The stock R33 fuel pump wiring is thin—upgrade it to at least 10-gauge wire with a 30-amp fuse to prevent voltage drop under load. For twin-pump setups, consider a surge tank arrangement to prevent cavitation during hard cornering.
Choosing the Right Larger Fuel Injectors
Injector sizing depends on your final horsepower goal, fuel type (pump gas vs. E85), and the boost level. For 500+ whp on pump gas, injectors in the 1000cc range are common. For E85 or higher ethanol blends, bump to 1300–1650cc to maintain proper duty cycles.
Injector Sizing Chart (Gasoline)
| Horsepower Target | Injector Size (cc/min) | Typical BSFC* |
|---|---|---|
| 500 whp | 850–1000 | 0.55 |
| 600 whp | 1000–1300 | 0.55 |
| 700 whp | 1300–1650 | 0.55 |
*Brake Specific Fuel Consumption – turbocharged engines typically use 0.55–0.60 lb/hp-hr.
High-Impedance vs. Low-Impedance
Most modern aftermarket injectors are high-impedance (saturated). These are easier to drive with stock ECUs and most piggyback or standalone systems. Low-impedance (peak-and-hold) injectors require a dedicated driver and are less common for street builds. Popular choices for R33 GT-Rs include Injector Dynamics ID1000/ID1300 and DeatschWerks DW1000/DW1300 – both provide excellent spray patterns and linear flow. For direct fit into the RB26 fuel rail, look for top-feed injectors with the proper connector style (Nissan/Nippondenso).
Fuel Rail Considerations
Stock R33 fuel rails can support modest injector upgrades, but at higher flow rates the internal cross-section becomes a bottleneck. Aftermarket billet rails (e.g., GReddy, Tomei, or custom) provide equal distribution to all six cylinders. If you choose a large injector (1000cc+), pair it with a fuel rail that has a -6 or -8 AN inlet and outlet for proper feed and return flow.
Fuel Pressure Regulator: Keeping Pressure Steady
A rising-rate or adjustable fuel pressure regulator (FPR) is essential when running higher-flow pumps and injectors. The FPR maintains a 1:1 rise with boost pressure, so the injectors see a constant differential pressure. Without a quality FPR, the rail pressure may spike under boost, causing rich or inconsistent fueling. Install a Fuelab, Aeromotive, or SARD pressure regulator with a gauge mounted in the engine bay. Mount it near the fuel rail with a short return line to the tank.
Fuel Lines, Fittings, and Surge Tanks
Stock Lines vs. Upgraded Hard Lines
The R33 GT-R leaves the factory with 5/16" (8mm) fuel lines. For 500+ whp, upgrade to at least 3/8" (10mm) or -6 AN feed and return lines. Aluminum or stainless braided PTFE hose is recommended for its resistance to ethanol corrosion and pressure. Replace the factory quick-disconnect fittings with AN-style adapters at the fuel rail and pump hanger.
Surge Tank / Lift Pump System
At very high power levels (700+ whp) or on track with low fuel levels, the stock in-tank pump can starve. A common solution is a surge tank fed by a low-pressure lift pump (Walbro 255) in the tank, with a high-pressure main pump (Walbro 450) pulling from the surge tank. Surge tanks from companies like Radium Engineering are designed for the R33 chassis and include built-in baffles. This setup eliminates fuel starvation and supports over 1000 whp.
Supporting Engine Bay Mods
Wiring Upgrade
High-flow fuel pumps draw significant current. The factory 12V feed wire (often 16-gauge) cannot handle 10+ amps continuously without voltage drop. Install a dedicated pump power harness with a 30A relay triggered by the ECU pump control wire. Use 10-gauge wire from the battery to the relay, and 12-gauge to the pump. This ensures the pump sees battery voltage under full load.
ECU Tuning
No fuel system upgrade works correctly without proper tuning. After fitting larger injectors and a higher-flow pump, the ECU's fuel maps, injector latency (dead-time), and volumetric efficiency tables must be recalibrated. A standalone ECU like a Haltech Elite 2500, Link G4+, or Motec M800 provides full control. If retaining the stock ECU, use a piggyback like a Nistune board or an Apexi Power FC with a tuned map. EcuTek also offers calibration support for R33 GT-Rs with aftermarket ECUs.
Putting It Together: A Sample 600 HP Fuel System Build
- Pump: Walbro 450 lph (F90000285) with hardwire kit and 10-gauge feed.
- Injectors: ID1300x (1300cc/min) for flexibility on E85 or pump gas.
- Regulator: Aeromotive 13109 (boost-referenced, 1:1).
- Rail: GReddy billet rail with -6 AN input and output.
- Lines: -6 AN PTFE feed and return lines from tank to rail.
- Tuning: Haltech Elite 2500 with fuel pressure sensor integrated.
- Additional: Dual-hanger or surge tank if tracking the car.
This combination has been proven to support 600+ whp on pump gas and 700+ whp on E85 with duty cycles under 80%.
Common Pitfalls to Avoid
- Undersized fuel return line: The stock return line is restrictive. A -6 return line is recommended for any pump over 255 lph. Without it, the FPR will not be able to bleed off excess pressure, raising rail pressure uncontrollably.
- Ignoring injector dead-time: Large injectors require significant latency compensation. Failure to tune dead-time causes lean/rich spikes during transitions.
- Using a pump without a pre-filter: Always install a 100-micron stainless mesh filter before the pump (or a 40-micron after the pump). This protects the injectors from debris.
- Neglecting fuel cooler: High-flow pumps generate heat, especially in a surge tank. In hot climates or during sustained high-load runs, a fuel cooler (bar-and-plate style) can keep fuel temperatures in check to prevent vapor lock.
Final Thoughts
A well-executed fuel system upgrade is the foundation of any 500+ HP R33 GT-R. Walbro pumps provide proven flow and reliability, larger injectors deliver the necessary volume, and the supporting modifications (regulator, lines, wiring, tuning) ensure everything works together seamlessly. Invest time in planning each component—fuel delivery errors are the most costly to fix after engine damage. With the right parts and a skilled tuner, your R33 will not only hit its power target but do so safely and consistently. For further reading, consult the Nissan Sports Magazine tuning archives or join the discussions on the GTR Register forum for real-world case studies.