Upgrading Fuel Pressure Regulator: Is It Worth It For Your Ev?

Owners of the Mitsubishi Lancer Evolution (Evo) frequently debate the need for an aftermarket fuel pressure regulator (AFPR). While some claim that the stock fuel pressure regulator is sufficient for most use cases, others argue that an upgrade is necessary when installing a fuel pump or pursuing a serious fuel system overhaul. Those in favour of an AFPR emphasise its ability to maintain consistent fuel pressure, which can prevent the engine from running rough. However, others counter that the stock FPR is adequate for up to 700 wheel horsepower and that an AFPR is only necessary when using larger fuel pumps or injectors. Ultimately, the decision to upgrade the fuel pressure regulator depends on individual performance goals and the specific modifications made to the vehicle.

When to upgrade your fuel pressure regulator

The fuel pressure regulator is a crucial component of your vehicle's fuel system, ensuring the injectors receive the right amount of fuel by maintaining steady fuel pressure. While upgrading this component may not be necessary for everyone, there are certain scenarios where an aftermarket fuel pressure regulator can bring significant benefits.

Upgrading your fuel pressure regulator is generally not required if you are making standard upgrades, such as installing a fuel pump or larger injectors. The factory or stock fuel pressure regulator in your vehicle is typically designed to handle these types of modifications without issue. However, there are situations where an aftermarket fuel pressure regulator becomes a worthwhile investment:

• Failure of the OEM Fuel Pressure Regulator: If your original equipment manufacturer (OEM) fuel pressure regulator fails or gives up, you may need to source an aftermarket replacement. This is especially true if finding a direct replacement unit is challenging or inconvenient.
• Aftermarket Fuel Rail Kit Installation: If you decide to install an aftermarket fuel rail kit, it may not have provisions for the stock fuel pressure regulator. In such cases, you will likely need to opt for an aftermarket fuel pressure regulator to ensure compatibility with your new fuel rail.
• Performance Modifications: If you are a performance enthusiast and plan to bore your engine blocks to a higher capacity or opt for turbo upgrades, you may need to increase the air-fuel ratio to prevent the engine from running lean. This requires a full-on fuel system upgrade, including a higher-flowing aftermarket fuel pressure regulator, to ensure the factory regulator does not become restrictive.
• High Horsepower Builds: For those aiming for very high horsepower builds (over 1000 HP), a purpose-built, high-quality aftermarket fuel pressure regulator is essential. These regulators are designed to handle the increased flow and pressure demands of such extreme performance setups.
• Fuel Type Compatibility: Some cheaper fuel pressure regulators may not be compatible with certain fuel types, such as ethanol or methanol. If you plan to use these fuel types, investing in a higher-end aftermarket regulator that can withstand these fuels is crucial to prevent engine damage.

While the stock fuel pressure regulator is often adequate for many applications, there are situations where an aftermarket upgrade can bring peace of mind and improved performance. It is always wise to prioritize safety when dealing with fuel systems, so investing in a quality, name-brand fuel pressure regulator can save you from costly engine failures in the long run.

Benefits of an adjustable fuel pressure regulator

Upgrading to an adjustable fuel pressure regulator (AFPR) can be beneficial for your Evo X, especially if you have modified your fuel system with an upgraded fuel pump or fuel injectors. Here are the benefits of an adjustable fuel pressure regulator:

Fine-Tuning Fuel Delivery

The primary benefit of an AFPR is the ability to fine-tune fuel delivery to your engine. The regulator allows you to increase or decrease fuel pressure, ensuring the optimal amount of fuel is supplied to the injectors. This can be crucial if you're running your engine at higher or lower pressures than stock, as the AFPR helps prevent engine starvation or flooding.

Improved Performance and Efficiency

By ensuring the correct air-fuel ratio, an AFPR can help improve engine performance and efficiency. This is especially beneficial if you've made other modifications to your fuel system, such as upgrading the fuel pump or injectors, as it allows you to maximise the potential of these upgrades.

Diagnostic and Monitoring Capabilities

AFPR kits often include fuel pressure gauges, allowing you to monitor your fuel pressure in real-time. This can be valuable for diagnosing fuel system issues and ensuring that your engine is running at the optimal fuel pressure.

Easy Installation

AFPR kits, such as the AMS EVO X Fuel Pressure Regulator Kit, are designed for easy installation and do not require any cutting or modifications to your vehicle. This makes upgrading your fuel pressure regulator a straightforward process.

Flexibility for Future Modifications

If you plan on making further modifications to your fuel system or engine, an AFPR provides the flexibility to adjust fuel pressure accordingly. This can save you from having to upgrade your regulator again in the future, as you can fine-tune the fuel pressure to match your engine's needs.

Mounting an adjustable fuel pressure regulator

• Research your fuel pump: Obtain basic information such as flow rate, maximum working pressure, and amperage draw. This information will help you choose the correct fuel pressure regulator for your system.
• Choose the right regulator: Select a regulator that is compatible with your fuel pump and fuel delivery system. Some fuel pumps have built-in regulators, so make sure you don't already have one before purchasing an external unit.
• Decide on the regulator style: There are two main styles of fuel pressure regulators: deadhead-style and bypass. Deadhead-style regulators are the simplest and most popular type, using a restriction to lower fuel pressure. Bypass regulators, on the other hand, bleed off excess fuel pressure and return it to the fuel tank, which can help improve performance and stability.
• Purchase the necessary components: In addition to the regulator, you may need to buy a few extra components to complete the installation, such as plumbing and mounting hardware.
• Mount the regulator: The regulator should be placed between the fuel pump and the carburetor or fuel injectors. The exact mounting location will depend on your vehicle's configuration and the type of regulator you are using. Some people choose to mount the regulator under the fuel tank, while others may find a different location that works better for their setup.
• Connect the regulator: Once the regulator is mounted, connect it to the fuel lines and any necessary vacuum or electrical lines. Make sure all connections are secure and tight to prevent leaks.
• Test the system: After installation, test the fuel pressure regulator to ensure it is working properly. Check for leaks, measure fuel pressure, and ensure that the regulator is providing stable fuel pressure.

By following these steps, you can successfully mount an adjustable fuel pressure regulator, which will help ensure a safe and reliable fuel system performance for your engine.

Recommended fuel pressure

The recommended fuel pressure for the Mitsubishi Lancer Evolution (EVO X) is 43.5 psi at idle. This is known as the base fuel pressure. However, when you are boosting 30 psi at wide-open throttle (WOT), the base fuel pressure will spike to around 73.5 psi.

You can adjust the base fuel pressure to be slightly higher to get more flow out of your injectors, but this has diminishing returns. Additionally, a very high base pressure can overrun a stock regulator at idle, causing the engine to run rich. Conversely, you can lower the base fuel pressure to control giant injectors at idle, but this requires a good fuel pressure regulator.

The stock fuel pressure regulator that comes with the EVO X should be sufficient for most users. However, if you are doing a serious fuel system overhaul, such as installing a surge tank or fuel cell with a new fuel rail and a large fuel pump, you may need to upgrade to an aftermarket fuel pressure regulator.

Injector sizing and fuel pressure

Fuel pressure also plays a crucial role in injector performance. Most injectors are rated at 43 psi, and higher fuel pressure increases flow rate, while lower pressure reduces it. This can be calculated using the formula: New PSI / Base PSI = Y. For instance, increasing fuel pressure from 43 psi to 58 psi would result in a 15% increase in flow rate. However, it's important to consider the limitations of the fuel delivery system, as higher pressure demands a larger volume of fuel and can strain the fuel pump.

When upgrading fuel injectors, it's essential to match the injector's electrical connector style (e.g., EV1, EV6, or Multec 2) to the vehicle's wiring harness. Additionally, the physical dimensions of the injector must be considered to ensure proper fitment.

In terms of fuel pressure regulators, opinions vary among Evo X owners. Some claim that the stock fuel pressure regulator is sufficient for most applications, while others suggest that an aftermarket regulator is necessary when installing a fuel pump or making significant fuel system modifications. It is recommended to consult with a professional or refer to manufacturer guidelines to determine the appropriate fuel pressure settings for your specific engine configuration.

Frequently asked questions