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

Product Description

Select the correct AEM adjustable fuel pressure regulator for your Honda or Acura fuel rail with one consolidated application guide covering AEM 25-300BK, 25-301BK, 25-303BK, and 25-304BK.

These regulators replace the factory-style rail-mounted fuel pressure regulator while adding adjustable fuel pressure, a 1:1 vacuum/boost reference, and the ability to retain the factory return hose or convert the return side to AN plumbing.

Quick Specifications

• Manufacturer: AEM Performance Electronics
• Product Type: Rail-mounted adjustable fuel pressure regulator
• Available Versions: 25-300BK, 25-301BK, 25-303BK, 25-304BK
• Material: CNC-machined 6061-T6 billet aluminum
• Finish: Black
• Fuel Pressure Adjustment: 20 PSI to the maximum capability of the fuel pump
• Vacuum / Boost Reference: 1:1
• Fuel Outlet: 9/16-18 ORB
• Return Plumbing: Factory-style hose or AN plumbing with appropriate adapter
• Installation: Mounts directly to the appropriate OEM Honda/Acura or AEM High Volume fuel rail
• Regulator Style: Bypass / return-style

Which AEM Regulator Do I Need?

The four regulators on this page share the same basic operating principle, but they use different rail-mount base and return configurations to fit different Honda and Acura fuel systems.

Do not choose the regulator only by vehicle chassis. Verify the engine, fuel rail, and regulator configuration installed in the car.

AEM 25-300BK

The 25-300BK is the common straight-return regulator configuration used across many 1990s Honda and Acura applications.

Common engine applications include:

• B16A2 / B16A3
• B18B1 / B18C1 / B18C5
• D15B7 / D15B8 / D15Z1
• D16Z6
• Select older Accord and Prelude applications

This includes many EG Civic, Del Sol, 1994-2001 Integra, and 1999-2000 Civic Si applications.

For B-Series applications, the 25-300BK pairs naturally with AEM fuel rails such as the AEM 25-103BK B16 Fuel Rail and AEM 25-100BK B18/B20 Fuel Rail where applicable.

AEM 25-301BK

The 25-301BK uses a different rail-mount configuration and is intended for applications including:

• D16Y5
• D16Y7
• B20Z2
• F20C1
• F22C1
• F23A1 / F23A4 / F23A5

Using an AEM 25-109BK D16Y7/D16Y8 fuel rail with a D16Y7 engine? Choose the 25-301BK.

AEM 25-303BK

The 25-303BK uses the angled-return regulator configuration and covers a different group of earlier Honda and Acura applications.

Common engine applications include:

• B17A1 / B18A1
• D15B6
• D16A1 / D16A6
• H22A / H23A applications
• Select Acura NSX, TL, and Vigor applications

Some H-Series and Prelude applications require the appropriate AEM High Volume Fuel Rail rather than the original Honda fuel rail.

For applicable H22/H23 combinations, see the AEM 25-104BK H-Series High Volume Fuel Rail.

AEM 25-304BK

The 25-304BK uses the offset/angled-return configuration for applications including:

• D16Y8
• B20B4
• F22B1
• F22B2

Using an AEM 25-109BK D16Y7/D16Y8 fuel rail with a D16Y8 engine? Choose the 25-304BK.

Using the AEM 25-109BK D-Series Fuel Rail?

If you arrived here from the AEM 25-109BK D16Y7/D16Y8 High Volume Fuel Rail, the choice is straightforward:

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

The D16Y7 and D16Y8 use the same AEM 25-109BK fuel rail, but they do not use the same rail-mounted regulator version.

Direct Rail-Mounted Regulator

The 25-300BK, 25-301BK, 25-303BK, and 25-304BK are designed to bolt directly to the appropriate Honda/Acura or AEM fuel rail in the traditional factory-style regulator location.

An O-ring seals the regulator to the fuel rail, while the regulator outlet handles the return side of the fuel system.

This makes these regulators an excellent option when you want adjustable fuel pressure without completely redesigning the fuel-system architecture around a remote universal regulator.

9/16-18 ORB Fuel Return Outlet

The regulator fuel outlet uses a 9/16-18 ORB (O-Ring Boss) connection.

AEM supplies the appropriate factory-style return fitting with the regulator, allowing many applications to retain the original rubber fuel-return hose.

For aftermarket AN return plumbing, AEM also offers:

• AEM 50-200-06: 9/16-18 ORB to -6AN male
• AEM 50-200-86: 9/16-18 ORB to -8AN male

The ORB connection seals with an O-ring rather than thread sealant.

Adjustable Fuel Pressure with 1:1 Boost Reference

AEM's Honda/Acura regulators allow the base fuel pressure to be adjusted from approximately 20 PSI up to the maximum pressure the fuel pump can provide.

The regulator also uses a 1:1 vacuum/boost reference. In a properly configured forced-induction system, fuel pressure rises one PSI for every one PSI of boost pressure applied to the regulator reference.

A fuel-pressure gauge should be used when setting or verifying base fuel pressure.

Interchangeable Return Orifice

AEM uses an interchangeable discharge-orifice system inside these regulators so the return-side flow characteristics can be matched to the fuel pump and overall fuel system.

A large discharge orifice is supplied in the regulator, with other configurations available when required for a specific fuel-system setup.

This is another reason the regulator should be selected and configured as part of the complete fuel system rather than treated as an isolated component.

Building a Larger JBtuned Fuel System?

The rail-mounted regulators on this page work extremely well when retaining a conventional Honda-style regulator arrangement.

However, when JBtuned builds many of our larger aftermarket feed-and-return fuel systems, we typically move to a different regulator architecture using the AEM 25-302BK Universal Adjustable Fuel Pressure Regulator.

The 25-302BK can be mounted directly alongside a compatible AEM fuel rail using the JBtuned Stainless-Steel O-Ring Boss to O-Ring Boss Adapter.

This gives JBtuned more flexibility in how the regulator, feed, and return plumbing are configured and is the regulator architecture we prefer for many higher-capacity complete fuel systems.

AEM rates both these Honda/Acura rail-mounted regulators and the 25-302BK for substantial fuel flow. The reason JBtuned moves to the 25-302BK on larger systems is primarily the flexibility of the complete aftermarket plumbing architecture rather than simply whether the original rail-mounted regulator physically fits.

Factory-Style Upgrade or Complete Fuel-System Build?

Choose one of the regulators on this page when you want an adjustable regulator that bolts directly to the appropriate Honda/Acura or AEM fuel rail while retaining the traditional rail-mounted regulator arrangement.

Consider the AEM 25-302BK + JBtuned ORB-to-ORB adapter when the regulator will become part of a larger JBtuned feed-and-return fuel system with upgraded fuel lines, filtration, pump capacity, and return plumbing.

Neither path is automatically right for every car. The correct configuration depends on the engine, rail, fuel pump, feed and return plumbing, fuel type, power requirements, and overall goals of the build.

Important Fitment Information

Honda and Acura used multiple fuel-pressure-regulator mounting and return configurations across different engines and model years.

Always select the regulator by verified engine and fuel-rail fitment rather than assuming that one Honda/Acura regulator fits every application.

Certain Accord and Prelude applications require the corresponding AEM High Volume Fuel Rail before an AEM rail-mounted regulator can be installed.

After installation or any fuel-system modification, pressurize the system and carefully inspect all fuel connections for leaks before starting or operating the engine.