Fuel Pressure Regulators: Holley's Restriction Number Explained

Holley fuel pressure regulators are designed to control the fuel pressure from the fuel pump to the carburetor. The restriction number on the Holley 12-803 and 12-803BP fuel pressure regulators is .220 (7/32) and .437 (7/16), respectively. These regulators feature adjustable fuel pressure settings, with the 12-803 offering a range of 4.5 to 9 psi and the 12-803BP offering the same range but with a different restriction number.

Adjustable fuel regulation

Holley's fuel pressure regulators are designed to precisely manage fuel pressure between the fuel pump and the carburetor. The ability to adjust fuel pressure is essential to prevent issues like flooding or drivability problems caused by excessive fuel pressure. By offering adjustable fuel regulation, Holley ensures that vehicle owners can fine-tune the fuel delivery according to their engine's specific requirements.

The Holley 12-803BP fuel pressure regulator, for instance, provides adjustable fuel regulation from 4-1/2 to 9 psi. It features 3/8" NPT inlet and outlet ports, along with a 3/8" NPT return port. This regulator is intended for systems with a return line back to the fuel tank and is designed exclusively for carburetor use.

Another example is the Holley 12-803 fuel pressure regulator, which offers a similar adjustable fuel regulation range from 4-1/2 to 9 psi. It comes with .220" (7/32") restriction, 3/8" NPT ports (1 inlet, 2 outlets), and a mounting bracket. This regulator is suitable for street/strip carbureted applications and helps prevent flooding by ensuring the fuel pressure matches the needle and seat assembly's requirements.

Holley's fuel pressure regulators cater to both carbureted and EFI fuel systems, providing a wide range of pressure options and both fixed and adjustable versions. The adjustability of these regulators makes them versatile and capable of accommodating various engine setups and performance goals.

In conclusion, the restriction number on Holley fuel pressure regulators, such as the 12-803 and 12-803BP, refers to the size of the restriction orifice, which is an essential component in managing fuel flow. Adjustable fuel regulation is a key feature of these regulators, allowing users to fine-tune fuel pressure to match their engine's needs and optimise performance. Holley's range of regulators offers flexibility and precision in fuel delivery for a variety of automotive applications.

NPT ports

The NPT (National Pipe Thread Taper) port is a type of fitting used in plumbing and hydraulic systems. It features a tapered thread that creates a seal between the male and female threads as they are tightened together. NPT ports are commonly used in fuel pressure regulators to connect fuel lines and other components.

Holley offers a range of fuel pressure regulators with different NPT port sizes to suit various applications. The standard NPT port size for Holley fuel pressure regulators is 3/8", which is found on the majority of their regulators, including the 12-803, 12-882, and low-pressure regulator options. This size is suitable for most fuel systems and provides a secure connection.

However, Holley also offers fuel pressure regulators with different NPT port sizes to cater to specific needs. For example, the Holley 12-803 regulator has one inlet and two outlet ports, all measuring 3/8" NPT. Additionally, they provide a 1/2" NPT option for applications that require larger fuel line connections. This larger port size ensures unrestricted fuel flow and is suitable for high-performance engines.

The NPT port size is an important consideration when choosing a fuel pressure regulator. It determines the size of the fuel line that can be used and plays a crucial role in ensuring proper fuel flow and system compatibility. Selecting the correct NPT port size is essential to achieving optimal performance and maintaining the health of the engine.

Return port

The return port is an essential component of a return style fuel pressure regulator, which operates differently from a deadhead system. In a return style regulator, the return port is marked as "Return" and is typically located on the bottom or opposite the inlet/outlet ports. This port allows excess fuel to be returned to the tank, maintaining the desired fuel pressure and reducing fuel temperature.

Understanding Return Style Regulators

Return style fuel pressure regulators are designed to maintain the desired fuel pressure by allowing excess fuel to flow back to the tank. Unlike deadhead systems, which are normally open, return style regulators are normally closed until the pressure limit is reached. When this limit is surpassed, the bypass outlet opens, returning the excess fuel to the tank. This design reduces the load on the fuel pump and helps prevent overheating, making it a preferred choice for street-driven cars.

The Role of the Return Port

The return port is specifically dedicated to returning excess fuel to the tank. It is one of the distinct ports found on a return style regulator, along with the inlet and outlet ports. By providing a path for the excess fuel to return, the return port plays a crucial role in regulating fuel pressure and preventing spikes that could lead to potential issues.

Installation and Compatibility

When installing a return style regulator, it is important to ensure that the return port is not blocked. Blocking the return port can lead to excessive fuel pressure and potential problems. The Holley 12-803BP fuel pressure regulator, for example, is designed with a 3/8" NPT return port, allowing for a return line back to the fuel tank. This regulator is intended for use with an electric fuel pump and a return line in the system. For mechanical fuel pumps, Holley recommends using the 12-803 regulator.

Benefits of Return Style Regulators

Return style fuel pressure regulators offer several advantages over deadhead systems. Firstly, they reduce the load on the fuel pump by circulating excess fuel back to the tank, which helps maintain fuel temperature. Secondly, they provide more mounting freedom as they can be placed upstream or downstream of the carburetor or EFI injectors. This flexibility allows for optimizing regulator performance and a quicker reaction to pressure changes.

Fuel pump compatibility

For carbureted applications, Holley's fuel pressure regulators, such as the 12-803 and 12-803BP, are designed to control fuel pressure from the fuel pump to the carburetor. These regulators feature adjustable fuel pressure settings, typically from 4.5 to 9 psi, and are compatible with electric fuel pumps with a return line. The 12-803BP, for example, has 3/8" NPT ports (1 inlet, 1 outlet, and 1 bypass or return) and is designed specifically for carburetor use.

On the other hand, some mechanical fuel pumps may not require a pressure regulator. Holley's classic Red vertical pump, for instance, is a low-pressure electric fuel pump designed to produce sufficient fuel pressure for a mild carbureted application without the need for a regulator.

For EFI applications, a regulator is typically required to accurately set the desired fuel pressure, especially for high-performance engines producing 450 hp or more. Holley offers EFI-compatible fuel pressure regulators, such as the PN 12-879 or 12-880, which can handle a wide range of fuel pressures from 4 to 65 psi.

It's important to note that the compatibility of a Holley fuel pressure regulator with a specific fuel pump depends on factors such as the fuel system type (carbureted or EFI), desired fuel pressure settings, and the presence of a return line. Therefore, when selecting a Holley fuel pressure regulator, it is essential to consider the specific requirements of your fuel system and choose a regulator that is compatible with your fuel pump and other system components.

Mounting bracket

The Holley Billet Regulator Bracket is a mounting bracket designed to fit 4150/4160 style carburetors. It is made of black anodized billet aluminium and simplifies the mounting of Holley fuel pressure regulators. The bracket mounts on the passenger side carb studs and is compatible with the Holley 12-803, 12-804, or 12-803BP fuel pressure regulator. The universal design fits both Holley and competitor carburetors.

The Holley Billet Regulator Bracket comes with the required hardware for easy installation. It measures 8.2 x 7.75 x 0.5 inches and has a clear or black anodized finish.

There are also other mounting brackets available for Holley fuel pressure regulators, such as the JEGS Billet Aluminum Regulator Bracket, the Moroso Fuel Regulator Mounting Brackets, and the Allstar Performance Fuel Regulator Bracket. These brackets are designed to fit specific Holley regulator models and carburetor types.

Frequently asked questions