The Walbro 255 Fuel Pump: In-Depth Specs & Performance Breakdown

The Walbro GSL392 (commonly known as the 255LPH) high-pressure fuel pump delivers reliable fuel flow up to 255 liters per hour (67 US gallons per hour) at key pressure points like 40 PSI and 73 PSI (3 and 5 Bar), making it a widely trusted choice for demanding applications requiring power levels typically in the 300-500+ wheel horsepower range. Built for durability and performance, its specifications provide a critical foundation for anyone modifying a vehicle's fuel delivery system.

Understanding the precise specifications of any automotive component is paramount when modifying your vehicle for increased performance. The Walbro 255, or Walbro GSL392 fuel pump, stands as one of the most popular and proven aftermarket high-flow fuel pumps globally. Its name, "255", directly references its nominal flow rate. Knowing its detailed specs goes far beyond just the headline flow number; it involves comprehending flow characteristics under pressure, electrical demands, physical dimensions, and material compatibility. This deep dive into the Walbro 255's specs provides the necessary information to make informed decisions and ensure reliable fuel system upgrades.

Key Walbro 255 Fuel Pump Specifications (GSL392 / F20000169)

  1. Flow Rate: This is the defining specification.

    • Nominal Flow: 255 Liters Per Hour (LPH) or 67 US Gallons Per Hour (GPH).
    • Flow @ 40 PSI (2.76 Bar): Approximately 255 LPH / 67 GPH (closely matching the nominal rating).
    • Flow @ 73 PSI (5.03 Bar): Approximately 150 LPH / 40 GPH. This demonstrates the significant impact of fuel pressure on flow. Higher pressure requires the pump to work harder against resistance, naturally reducing the volume delivered.
    • Flow @ 100 PSI (6.9 Bar): Approximately 85 LPH / 22.5 GPH. This further highlights the pressure dependency. While capable of pressures this high, flow diminishes considerably.
    • Context: The quoted flow rates (255 LPH @ 40 PSI) provide a baseline. Actual flow in your vehicle depends heavily on the entire fuel system setup – fuel pressure regulator type and setting, inlet restrictions, fuel line size and condition, and voltage supply stability.

  2. Operating Pressure Range:

    • Maximum Pressure: Up to 115 PSI (7.9 Bar). This indicates the pump's capability to generate high pressure, primarily important for applications using a referenced fuel pressure regulator where pressure rises with boost.
    • Continuous Duty Pressure: The pump is designed to operate reliably at pressures commonly found in EFI systems, typically up to 80-100 PSI in boosted applications. Sustained operation very close to the absolute maximum pressure may impact long-term durability.

  3. Voltage Requirements:

    • Nominal Voltage: Designed to operate on 12 Volts DC.
    • Operating Voltage Range: Approximately 6 Volts to 16 Volts. The pump can start and run at voltages as low as 6V, ensuring operation during cranking when system voltage drops. It can tolerate brief voltage spikes up to 16V. However, sustained low voltage significantly reduces flow rate and output pressure.
    • Critical Note: The Walbro 255 is highly sensitive to voltage. A drop in system voltage directly translates to a significant drop in pump performance (both flow and pressure). Adequate wiring (often requiring an upgraded relay and power/ground wiring kit) is essential to maintain stable voltage at the pump connector under full load.

  4. Amperage Draw & Power:

    • Amperage Draw @ 13.5V: Approximately 8-10 Amps under typical load conditions. Peak current draw can be slightly higher on startup or under maximum pressure load.
    • Amperage Draw @ 12V: Increases due to reduced efficiency at lower voltage.
    • Power Consumption: Around 110-135 Watts at 13.5V.
    • Why It Matters: This amperage draw necessitates checking the vehicle's existing fuel pump wiring circuit. Standard factory wiring may not be thick enough to handle 8-10+ amps without excessive voltage drop over the length of the wire run, especially if the factory pump drew significantly less. Upgrading wiring is frequently required.

  5. Fuel Compatibility & Temperature:

    • Gasoline: Fully compatible.
    • Ethanol Blends (E10, E15): Fully compatible and widely used in such applications.
    • Higher Ethanol Blends (E85, E100): Designed and rated for continuous use with E85 and E100 ethanol fuels. Walbro pumps are known for their resistance to ethanol corrosion and wear.
    • Operating Temperature: Designed to operate submerged in fuel, tolerating fuel temperatures encountered in standard fuel tanks. The fuel itself acts as coolant and lubricant.

  6. Physical Dimensions:

    • Overall Pump Length: Approximately 155mm (6.1 inches) including the lower strainer cup and top electrical connector.
    • Pump Body Diameter: Approximately 34mm (1.34 inches).
    • Electrical Connector: Uses the industry-standard "German" Bosch style two-pin flat connector found on many fuel pumps.
    • Strainer Diameter: Designed to fit common in-tank fuel pump assemblies and hanger baskets (e.g., Ford Mustang, Nissan 240SX, Subaru STI, Mitsubishi EVO, Volkswagen GTI, Honda Civic, etc.). It often includes a universal mesh filter sock that may need adapting or replacement to match the vehicle's existing strainer fitting.
    • Inlet/Outlet: Features a rigid 3/8" (approximately 10mm) barbed outlet port and an inlet port covered by the strainer sock.

Interpreting Walbro 255 Flow Rate Specs

The advertised 255 LPH flow rate is measured under specific conditions: typically at 12 volts (though sometimes 13.5v industry standard) and 40 PSI (free flow with minimal backpressure can be higher). This flow rate indicates the pump can deliver enough fuel for significant horsepower gains. However, three critical factors dramatically affect real-world flow delivered to the injectors:

  1. System Fuel Pressure: This is the single biggest factor. Doubling the pressure roughly halves the flow (not perfectly linear, but significant). An engine requiring 50 PSI base pressure will get less flow than one running 43.5 PSI. A turbocharged engine using a 1:1 rising rate regulator will see pressure climb significantly with boost. For example, at 25 PSI boost, fuel pressure might be 43.5 (base) + 25 = 68.5 PSI. The Walbro 255 flow at ~70 PSI is substantially lower than at 40 PSI. Matching the pump's output to the target pressure is crucial.
  2. Electrical Voltage: As mentioned, voltage drops are performance killers. A drop from 13.5V to 11.5V at the pump connector can reduce flow by 20% or more. Thin factory wiring, corroded connectors, or aging relays cause this. Reliably achieving the pump's rated specs requires excellent voltage supply.
  3. System Restriction: Blocked strainer socks (due to debris or fuel tank corrosion), kinked or undersized fuel lines, or restrictive filters upstream of the pump can reduce flow. Restrictions on the outlet side (like small diameter lines or filters) primarily increase the system pressure the pump must overcome, which then reduces flow as explained in point 1.

Performance Capability: How Much Power?

While marketing often lists broad horsepower ranges, the actual power a Walbro 255 supports depends heavily on the factors above and the specific engine setup:

  • Voltage Matters: Performance figures assume a good 13.5-14V supply.
  • Fuel Pressure: What pressure is the system operating at? A naturally aspirated engine at 43 PSI will have much more flow headroom than a turbo engine at 70 PSI.
  • Injector Duty Cycle: Conservative tuning targets 80% injector duty cycle, while some setups push closer to 90-95% for brief periods.
  • Brake Specific Fuel Consumption (BSFC): How efficiently does the engine use fuel? High boost, methanol injection, or specific engine designs change fuel needs. Performance engines often have a higher BSFC (require more fuel per HP).
  • Common Estimate: With stable voltage (13.5V+) at the pump and moderate fuel pressure (<65 PSI), the Walbro 255 can safely support approximately 350-500+ wheel horsepower on gasoline depending on BSFC, injector sizing, and duty cycle. For E85, which requires ~30% more fuel volume than gasoline, the realistic support range drops to roughly 250-350+ wheel horsepower under the same pressure conditions due to the higher volume demand. Pushing pressures towards 80 PSI or above significantly reduces the safe power ceiling.

Durability & Material Quality

The Walbro 255 earns its reputation for reliability due to robust construction:

  • Materials: Features a high-strength permanent magnet motor, hardened stainless steel internals (impellers, commutators, bearings), and resistance components designed to withstand modern fuels, including ethanol.
  • Design: Incorporates sophisticated internal fluid channels for motor cooling and component lubrication. Continuous operation while fully submerged in fuel ensures temperature control.
  • Testing: Pumps undergo rigorous performance and endurance testing under simulated operating conditions.
  • Manufacturing: Precision manufacturing standards ensure consistent quality and performance across the product line. Counterfeit pumps remain a significant issue, highlighting the importance of sourcing genuine pumps from authorized distributors.

Applications & Installations

The Walbro 255 is an extremely common upgrade or replacement pump. Key applications include:

  • Performance Upgrades: Turbocharging, supercharging, nitrous oxide, high-compression NA builds in popular platforms like Honda/Acura, Subaru WRX/STI, Mitsubishi EVO, Nissan 240SX/350Z/Skyline GT-R, Mazda RX-7/Miata, Toyota Supra/MR2, BMW 3-series, Ford Mustang, Chevrolet Camaro, Volkswagen/Audi.
  • OEM Replacement: Used as a high-quality replacement for original failing pumps in numerous vehicles, often providing a flow margin over the stock pump. Its physical compatibility with many stock baskets and assemblies makes it popular.
  • Installation Notes:
    • Voltage Is Key: Mandatory wiring upgrades (relay kit with 10- or 12-gauge power wire directly from the battery to the pump, solid ground) are highly recommended for performance applications and often even for stock replacement in vehicles known for voltage drop. This ensures the pump can perform as per its specs.
    • Filtration: Always install the pump with a new, clean, and correctly sized strainer sock at the inlet. Install a new, high-flow fuel filter after the pump to protect injectors.
    • Orientation: Designed for vertical operation, submerged in fuel. Improper mounting angles can lead to premature wear or starvation.
    • Sealing: When installing into an assembly or hanger basket, ensure all gaskets and seals are replaced correctly to prevent leaks and pressure loss.

Walbro 255LPH vs. Other Options

Understanding how the Walbro 255 compares helps in selection:

  • Stock Replacement (e.g., OE spec, lower flow Walbros like F20000026): The 255 provides a significant flow increase over most stock pumps. A valuable upgrade even if not initially needed for max power, offering headroom and peace of mind.
  • Higher Flow Pumps (e.g., Walbro F90000267 "450LPH", Bosch 044, DW/DSS 300+): These pumps flow substantially more, especially at higher pressures (e.g., > 70 PSI), supporting higher power levels (500-700+ WHP). They typically draw significantly more current (15-20+ Amps), generate more noise and heat, and cost more. They are necessary when the Walbro 255's flow and pressure capabilities are exceeded by the engine's fuel demands. Choosing a pump significantly oversized for the application can shorten its lifespan and cause unnecessary electrical load.
  • "Fake" Walbros: The market is flooded with counterfeit Walbro 255 pumps. These often fail prematurely, flow less than advertised, and lack the material quality. Buy from highly reputable, authorized dealers. Genuine pumps have specific markings and build characteristics (see Walbro's website for counterfit identification guides).

Conclusion: Leveraging the Walbro 255's Specifications

The Walbro 255 fuel pump remains a cornerstone of fuel system modifications due to its proven performance envelope, durability with modern fuels, and relatively simple installation requirements. Its specifications – most critically the 255 LPH flow at 40 PSI and 150 LPH at 73 PSI – define its capability for a wide range of popular performance builds and high-quality stock replacements. However, achieving its rated performance consistently demands careful attention to electrical supply and fuel system integrity. Understanding the impact of voltage and pressure on its flow curve is essential for proper application and avoiding fuel starvation at critical moments. When installed correctly with adequate wiring, the genuine Walbro 255 provides a robust and reliable foundation for numerous fuel delivery needs.

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