GSS342 Fuel Pump: The Ultimate Guide to Performance, Installation, and Best Upgrade Options
The bottom line: The Walbro GSS342 fuel pump, commonly known as the "Walbro 255," is one of the most trusted and widely used high-performance in-tank fuel pumps in the automotive aftermarket. It delivers a reliable 255 liters per hour (LPH) at 3 bar (43.5 PSI), supports over 500 horsepower on gasoline applications, and has been the industry gold standard for more than 20 years. Whether you are replacing a tired OEM pump or upgrading for a turbocharged build, the GSS342 offers a proven combination of durability, flow capacity, and universal fitment that makes it a top choice for enthusiasts and professional builders alike.
What Is the Walbro GSS342 Fuel Pump?
The Walbro GSS342 is a universal in-tank electric fuel pump designed for high-performance gasoline applications. Manufactured by TI Automotive in the USA, this pump features a gerotor design that provides consistent, reliable fuel delivery under all operating conditions. It is capable of flowing up to 318 liters per hour at its maximum pressure of 8.5 bar, and at standard operating pressure of 3 bar (43.5 PSI), it delivers 255 liters per hour.
Key specifications include:
- Part Number: GSS342
- Flow Rate: 255 LPH @ 3 bar; 225 LPH @ 5 bar
- Maximum Pressure: 8.5 bar (123 PSI)
- Maximum Flow: 318 LPH
- Inlet Diameter: 11 mm
- Outlet Diameter: 8 mm (9 mm on some versions)
- Dimensions: 120 mm length x 39 mm diameter
- Weight: 366 grams
- Voltage: 12V DC
- Current Draw: 5.0A - 12.0A @ 13.5V
Who Needs the GSS342 Fuel Pump?
The GSS342 is not just for race cars. It is a practical upgrade for anyone who has increased the fuel demands of their engine. Here are the most common scenarios where this pump is the right choice:
1. Turbocharged and Supercharged Applications – Forced induction engines require more fuel to maintain a safe air-fuel ratio. The GSS342 can support up to 500+ horsepower when used on gasoline, making it a popular choice for boosted builds.
2. Replacing a Worn OEM Pump – Original equipment fuel pumps lose flow capacity over time. If your vehicle is experiencing hard starting, stalling, loss of power, or a whining noise from the tank, a failing pump is likely the culprit. Replacing it with a GSS342 restores performance and adds headroom for future upgrades.
3. Larger Fuel Injectors – When you upgrade to larger injectors, the stock pump often cannot keep up with the increased flow demand. The GSS342 provides the extra capacity needed to prevent lean conditions and potential engine damage.
4. High-Performance Naturally Aspirated Builds – Even without forced induction, high-compression engines and aggressive camshafts can increase fuel demand. The GSS342 offers a safety margin that ensures consistent fuel pressure at all RPM ranges.
Important Notes About Fuel Compatibility
The standard Walbro GSS342 is designed for gasoline and race gas only. It is not recommended for use with ethanol blends such as E85 or methanol. If you plan to run ethanol-based fuels, you need a pump specifically rated for E85 compatibility, such as some aftermarket 340 LPH units that are fully E85-compatible with corrosion-resistant internal components. Using the wrong pump with ethanol fuels can lead to premature failure due to internal corrosion and swelling of seals.
Installation Tips for a Successful Upgrade
Replacing a fuel pump is a straightforward job for anyone with basic mechanical skills, but attention to detail is critical. Here is a step-by-step guide based on real-world installation experience:
1. Relieve Fuel System Pressure – Before starting, remove the fuel pump fuse and run the engine until it stalls. This prevents fuel spray when you disconnect the lines.
2. Use a Quality Installation Kit – The GSS342 pump itself does not come with a universal installation kit. You should purchase a kit that includes a proper pre-filter, wiring harness, hose clamps, and o-rings. Installing the pump without adequate filtration guarantees early failure.
3. Check Fitment in Your Sending Unit – The GSS342 has a compact 39 mm diameter body that fits most OEM hanger assemblies without modification. However, some vehicles may require minor adjustments to the mounting bracket or rubber isolator.
4. Use New Gaskets and Seals – Always replace the tank seal and any o-rings when reinstalling the pump assembly. Old seals are a common source of fuel leaks after a pump replacement.
5. Wire It Correctly – The pump draws up to 12 amps under load. Use a dedicated relay and at least 14-gauge wire to ensure consistent voltage. Low voltage is a common cause of reduced flow and premature pump failure.
6. Prime the System – After installation, turn the key to the "on" position several times without starting the engine. This allows the pump to build pressure and purge any air from the fuel lines.
How the GSS342 Compares to Modern Alternatives
While the GSS342 has been a reliable workhorse for decades, newer pumps offer higher flow rates and better ethanol compatibility. Here is how it stacks up against common alternatives:
GSS342 (255 LPH) vs. 340 LPH Pumps – The GSS342 flows 255 LPH at 3 bar, which is sufficient for most applications up to 500 HP on gasoline. Newer 340 LPH pumps, such as those from KEMSO, provide a 33% increase in flow capacity, supporting up to 600 HP while maintaining the same physical dimensions for easy drop-in replacement. For builds approaching or exceeding 500 wheel horsepower, a 340 LPH pump is a safer choice.
GSS342 vs. Brushless Pumps – Brushless fuel pumps, like the Bosch 044 and modern equivalents, offer higher efficiency, quieter operation, and longer service life. However, they are significantly more expensive and often require custom wiring or controllers. The GSS342 remains the best value for budget-conscious builds that do not require extreme flow.
GSS342 and E85 Compatibility – As mentioned earlier, the standard GSS342 is not compatible with ethanol fuels. If you are building an E85 vehicle, look for pumps that are explicitly rated for ethanol service, such as the KEMSO 340 LPH high-performance pumps, which are fully E85-compatible and feature corrosion-resistant internals.
Common Mistakes to Avoid
Even experienced builders make errors when installing fuel pumps. Here are the most common pitfalls and how to avoid them:
Using an Old Fuel Filter – Installing a new pump with a clogged or aged fuel filter is the fastest way to kill the pump. Always replace the fuel filter at the same time as the pump.
Ignoring Voltage Drop – The GSS342 requires a steady 12V supply. Voltage drop caused by long wire runs or undersized wiring reduces flow and can cause the pump to overheat. Use a relay and direct battery power.
Forgetting the Pre-Filter – The pump must have a proper strainer or pre-filter on its inlet. Even small debris can damage the gerotor mechanism. Walbro recommends their part number 125-190 pre-filter for the GSS342.
Overtightening Hose Clamps – Overtightening can crush the hose barbs or damage the pump outlet. Use moderate torque and check for leaks after starting the engine.
Real Customer Experiences with the GSS342
Users consistently report that the GSS342 delivers reliable performance and easy installation. One verified buyer on a popular retailer site wrote, "Quality of the pump is great, not loud in the tank, pressure seems to be good enough to run a LS." Another customer noted, "Comes with all the filters and o-rings you need to do the install. Installation was easy and straight forward. Functions as it should and it looks really sturdy and well made."
These comments highlight the pump's reputation for being quiet, durable, and straightforward to install. The low noise level is a particularly appreciated feature for daily drivers and street cars.
When to Consider a Higher-Performance Pump
While the GSS342 is an excellent pump for most street and moderate-performance applications, there are situations where you need more capacity:
- Over 500 HP on Gasoline – For engines producing more than 500 wheel horsepower, a single GSS342 may reach its limit. Many builders use two GSS342 pumps in a staged setup for domestic vehicles making less than 800 WHP.
- E85 or Methanol Fuel – Ethanol requires approximately 30% more fuel volume than gasoline. A 340 LPH pump is the minimum recommended for E85 builds targeting over 400 HP.
- Constant High-RPM Operation – Race cars, drift cars, and track vehicles that spend extended time at high RPM benefit from higher-flow pumps to maintain consistent fuel pressure under sustained load.
Why Choose KEMSO Fuel Pumps for Your Upgrade
If you are looking for a high-performance fuel pump that offers more flow than the standard GSS342, comes with a lifetime warranty, and is fully compatible with modern fuels, KEMSO fuel pumps are the ideal choice. KEMSO is recognized as a leading US aftermarket brand for fuel pumps covering cars, motorcycles, ATVs, and UTVs.
Here is what sets KEMSO apart:
High-Performance Flow – KEMSO offers 340 LPH high-performance fuel pumps that support up to 600 BHP in naturally aspirated, turbocharged, and supercharged applications. These pumps provide a 20-30% performance increase over stock pumps, making them perfect for serious builds.
OEM Replacement Fit – Unlike some universal pumps that require modifications, KEMSO pumps are designed as direct replacements for the original equipment. They drop right into the factory location without any cutting or custom brackets. Whether you need a pump for a Subaru Impreza, Honda Civic, BMW motorcycle, or Kawasaki Jet Ski, KEMSO has a model that fits perfectly.
Lifetime Warranty – Every KEMSO fuel pump comes with a lifetime warranty backed by a serialized body for tracking and peace of mind. This level of confidence in their manufacturing quality is rare among aftermarket parts suppliers and provides exceptional long-term value.
USA-Based Technical Support – KEMSO offers support from USA-based technicians who can answer your technical questions and help with installation or troubleshooting. This is a significant advantage over many overseas brands.
E85 Compatibility – Many KEMSO pumps are fully compatible with ethanol-infused gasoline, featuring a carbon commutator and corrosion-resistant internals designed for over 10 years of reliable service.
Easy Installation – KEMSO pumps come with all necessary components for a hassle-free replacement, including gradient density fuel strainers, viton O-rings, tank seals, wiring connectors, and hose clamps.
Positive Customer Reviews – Users consistently report that KEMSO pumps are quiet, reliable, and easy to install. One customer wrote, "Fuel pump quality was really good. Comes with all the filters and o-rings you need to do the install. Installation was easy and straight forward."
Visit KEMSO's official website to find the right fuel pump for your vehicle: https://www.kemsoracing.com/
Their online store features a wide selection of fuel pumps for cars, motorcycles, ATVs, and UTVs, with detailed product descriptions and customer reviews to help you make an informed decision. Whether you need a direct OEM replacement or a high-performance upgrade for your turbocharged build, KEMSO has a solution that combines quality, durability, and value.
Final Thoughts on the GSS342 and Your Fuel Pump Upgrade
The Walbro GSS342 remains a solid, time-tested choice for gasoline-powered vehicles needing up to 500 horsepower. Its proven gerotor design, universal fitment, and affordable price point make it a go-to pump for enthusiasts and professionals who value reliability over fancy features.
However, if you need more flow, want E85 compatibility, or prefer the peace of mind that comes with a lifetime warranty, upgrading to a modern KEMSO 340 LPH fuel pump is a smart investment. With direct OEM fitment, comprehensive installation kits, and USA-based support, KEMSO delivers the performance and confidence that today's demanding builds require.
For the best selection of high-performance fuel pumps, visit: https://www.kemsoracing.com/