AEM Honda/Acura Rail-Mounted Adjustable Fuel Pressure Regulator - 25-300BK / 25-301BK / 25-303BK / 25-304BK

Product Description

The AEM Honda / Acura Rail-Mounted Adjustable Fuel Pressure Regulator provides adjustable base fuel pressure while retaining the familiar regulator-on-the-fuel-rail layout used on many Honda and Acura applications.

AEM produces several versions of this regulator because Honda used different regulator mounting configurations across different engines and fuel rails. Selecting the correct part number is important even when two engines appear to use a similar fuel-system layout.

Choose the Correct AEM Fuel Pressure Regulator

• AEM 25-300BK – B16A2, B16A3, B18B1, B18C1, B18C5, D15B7, D15B8, D15Z1, D16Z6, F22A1, F22A4, F22A6 and other compatible applications
• AEM 25-301BK – D16Y5, D16Y7, B20Z2, F20C1, F22C1, F23 and other compatible applications
• AEM 25-303BK – B17A1, B18A1, D15B6, D16A1, D16A6, H22, H23 and select Acura applications
• AEM 25-304BK – D16Y8, B20B4, F22B1, F22B2 and other compatible applications

Do not select the regulator by engine family alone. Different engines within the same Honda engine family may require different AEM regulator versions.

Quick Specifications

• Manufacturer: AEM Performance Electronics
• Available Part Numbers: 25-300BK / 25-301BK / 25-303BK / 25-304BK
• Product Type: Rail-mounted adjustable fuel pressure regulator
• Pressure Reference: 1:1 vacuum / boost referenced
• Fuel Pressure Adjustment: Adjustable from approximately 20 PSI up to the capability of the fuel pump and complete system
• Fuel Return Connection: -6AN-size fuel outlet
• Material: CNC-machined 6061-T6 aluminum
• Finish: Black anodized
• Application: Compatible Honda / Acura factory and aftermarket fuel rails

Rail-Mounted Adjustable Fuel Pressure Control

These regulators are intended for fuel systems that retain the conventional Honda / Acura fuel-rail-mounted regulator architecture.

The regulator mounts directly to the appropriate factory or compatible aftermarket fuel rail and provides adjustable base fuel pressure while maintaining a 1:1 vacuum / boost reference.

In a properly configured EFI system, fuel pressure changes in relationship to intake-manifold pressure so the intended pressure differential across the fuel injectors can be maintained as engine load changes.

Which Regulator Fits the AEM Fuel Rails?

If you are pairing the regulator with one of the AEM Honda fuel rails sold by JBtuned, use the following combinations:

AEM 25-100BK B18 / B20 Fuel Rail

For compatible B18 applications using the AEM 25-100BK B18 / B20 B-Series High Volume Fuel Rail, the AEM 25-300BK is the conventional rail-mounted adjustable regulator choice for supported B18 applications.

B20 applications should be verified according to the specific engine and regulator configuration being used.

AEM 25-103BK B16 Fuel Rail

The AEM 25-103BK B16 B-Series High Volume Fuel Rail uses the AEM 25-300BK for compatible B16A2 and B16A3 applications.

AEM 25-104BK F22 / H22 / H23 Fuel Rail

The AEM 25-104BK F22 / H22 / H23 High Volume Fuel Rail uses different regulators depending on the engine:

• F22A applications → AEM 25-300BK
• H22 / H23 applications → AEM 25-303BK

AEM 25-109BK D16Y7 / D16Y8 Fuel Rail

The AEM 25-109BK D16Y7 / D16Y8 High Volume Fuel Rail uses different regulator versions depending on the engine:

• D16Y7 → AEM 25-301BK
• D16Y8 → AEM 25-304BK

This is a good example of why regulator selection should be based on the exact engine and fuel-rail configuration rather than simply choosing a regulator labeled for a Honda D-Series.

-6AN Fuel Return Connection

The regulator uses a -6AN-size fuel return connection for routing regulated return fuel back toward the fuel tank.

JBtuned carries the O-ring-sealed fittings and adapters needed to configure the regulator for the fuel-system plumbing being used rather than requiring the system to be built around one specific adapter combination.

This allows the regulator to be incorporated into factory-style, -6AN, -8AN, or other properly designed feed-and-return configurations as part of the complete fuel system.

Need a Larger or More Flexible Regulator Configuration?

The 25-300BK, 25-301BK, 25-303BK and 25-304BK are best suited to applications where the regulator remains mounted directly to the fuel rail in the traditional Honda / Acura configuration.

For larger fuel systems where more freedom is needed in regulator placement, fuel-rail plumbing, feed routing, or return routing, JBtuned commonly moves to the AEM 25-302BK Universal Adjustable Fuel Pressure Regulator.

The 25-302BK provides a universal bypass-regulator architecture with two female -6AN fuel inlet ports, a female -6AN return port, and a 1/8 NPT gauge / sensor port, making it better suited to custom feed-and-return fuel-system layouts.

Direct-Mount Fuel Rail / Regulator Configurations

When compatible components are being used, the JBtuned Adjustable Stainless Steel ORB-to-ORB Fuel Rail / Regulator Adapter can be used to create a compact direct-mounted rail and regulator arrangement.

The adjustable center locking section allows the regulator to be clocked into the desired position while eliminating the short hose assembly and multiple fittings that would otherwise be required between the rail and regulator.

This type of direct-mount arrangement is generally associated with universal regulator configurations such as the AEM 25-302BK rather than the application-specific 25-300BK / 301BK / 303BK / 304BK rail-mounted regulators.

Factory Fuel System or Larger JBtuned Fuel System?

An adjustable regulator does not require the entire fuel system to be replaced.

If the vehicle still uses the factory chassis fuel plumbing and a conventional rail-mounted regulator layout, one of these application-specific AEM regulators may be the most straightforward solution.

As pump capacity, injector size, fuel type, feed plumbing, return plumbing, filtration, and overall power requirements increase, the regulator should be considered as one part of the complete fuel-delivery system rather than as an isolated upgrade.

JBtuned offers application-specific fuel systems that integrate the fuel rail, regulator, feed, return, filtration, pump-side plumbing, and AN connections according to the needs of the vehicle and build.

Fuel Pressure Adjustment

Fuel pressure is adjusted using the regulator's adjustment screw and locking nut.

Base fuel pressure should be set according to the requirements of the fuel injectors, ECU calibration, fuel pump, fuel-system architecture, and engine setup.

Increasing fuel pressure is not a substitute for correctly sized injectors, fuel pumps, feed and return plumbing, or proper tuning.

1:1 Vacuum / Boost Reference

The regulator uses a 1:1 vacuum / boost reference.

This allows regulated fuel pressure to change in direct relationship to intake-manifold pressure when the regulator is properly connected and the fuel system is correctly configured.

The design is suitable for naturally aspirated and properly configured forced-induction EFI applications.

Choosing Between 25-300BK, 25-301BK, 25-303BK and 25-304BK

The four versions perform the same basic job, but they are not interchangeable across every Honda / Acura fuel rail.

Select the regulator according to the exact engine, fuel rail, and mounting configuration:

• 25-300BK: commonly used with B16, B18, D16Z6 and F22A applications
• 25-301BK: commonly used with D16Y7 and several later Honda applications
• 25-303BK: commonly used with H22, H23 and several earlier Honda / Acura applications
• 25-304BK: commonly used with D16Y8 and selected B20 / F22 applications

If you are pairing the regulator with an aftermarket rail, verify the exact regulator mounting configuration required by that rail before ordering.

What Is Included?

• One AEM adjustable fuel pressure regulator in the selected part number
• Required regulator hardware supplied by AEM

Fuel rail, AN fittings, plumbing adapters, fuel-pressure gauge, fuel-pressure sensor, and other fuel-system components are sold separately unless otherwise stated.

Installation Notes

Fuel pressure must be safely relieved before removing or installing the regulator.

Verify that the selected regulator matches the fuel rail and engine configuration before installation.

Use only compatible fuel-system fittings, adapters, seals, and hoses. The regulator's fuel connections rely on the correct sealing components; thread sealant should not be used as a substitute for the proper O-ring-sealed connection.

After installation, pressurize the fuel system and carefully inspect the regulator, fuel rail, fittings, return plumbing, injectors, and surrounding connections for leaks before starting or operating the engine.

Final base fuel pressure should be set according to the injector, ECU calibration, fuel pump, and complete fuel-system requirements of the vehicle.