Fuel Pressure Regulator By-Pass Style

The Holley fuel pressure regulator by-pass style (model 12-803BP) is an essential inline fuel management component for carbureted and naturally aspirated fuel systems operating in the 4.5 to 9 psi range. This polished aluminum regulator serves as a critical upgrade for hot rod builders, carburetor enthusiasts, and performance mechanics who demand precise fuel delivery without expensive fuel pump modifications. Whether you're building a classic street machine, fine-tuning a weekend cruiser, or dialing in a show car with traditional carburetion, this by-pass style regulator maintains consistent fuel pressure while safely returning excess fuel to the tank.

The by-pass design operates by opening an internal valve when system pressure exceeds the target threshold, allowing excess fuel to return through the dedicated 3/8 inch NPT return port directly to the fuel tank. This architecture eliminates fuel line backpressure and prevents carburetor flooding, a common problem when stock fuel pumps deliver more volume than needed. Constructed from durable aluminum with a polished finish, the regulator features three 3/8 inch NPT ports—inlet, outlet, and return—enabling straightforward integration into most fuel system configurations. The compact 3.55 x 2.65 x 3.65 inch footprint fits easily in engine bays without requiring extensive plumbing rework, and the lightweight 0.68 lb design adds negligible weight to your build.

Mechanics and fabricators favor the Holley 12-803BP for carburetor conversions, engine swaps, and fuel system upgrades where pump output exceeds carburetor demand. The 4.5 to 9 psi operating window suits most four-barrel and two-barrel carburetors, making installation straightforward for those upgrading vintage fuel systems or installing modern high-volume pumps on older platforms. Installation requires basic plumbing skills and standard hose fittings; most technicians complete the job in under an hour. Compatible with gasoline engines and ideal for street-driven vehicles, show cars, and vintage restorations, this by-pass regulator delivers the reliability and tuning capability serious enthusiasts expect from Holley performance components.