The Radium Engineering FHST (fuel hanger surge tank) is compatible with all BMW E90/91/92/93 3-series with the N54 or N55 engine.
NOTE: This system is compatible with the E90/91/92/93 M3 fuel tank. However, because the M3 uses a brushless fuel pump, the installer must devise a solution for triggering the new surge tank fuel pump(s). This is not covered in the installation instructions. Also, because of the exhaust system, the fuel feed kits are NOT compatible with the M3.
Overview
The Radium Fuel Hanger Surge Tank is a revolutionary way to eliminate fuel starvation that can occur during high-performance driving, while also providing a way to upgrade the fuel pumps for high-horsepower engine modifications. This system is installed inside the BMW fuel tank on the opposite side of the factory fuel pump and can hold one or two high-flow aftermarket fuel pumps. The OEM fuel pump is used to pump fuel into the FHST, while the pumps inside the FHST supply fuel to the engine. The system is E85 compatible and does not require any permanent modifications for installation.
Read below to see how the FHST works.
BMW Fuel Tank
The OEM saddle bag fuel tank is quite complex. The venturi jet pump is driven by the feed line instead of the return (M3 has 2 venturi jet pumps). The post pump filter and FPR are integrated into the LH side of the tank where the FHST mounts.
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Radium FHST
When these BMWs experience high lateral Gs, they inherently suffer from fuel slosh. The FHST is the best solution for preventing fuel starvation. As described below, the FHST pump(s) are supplied with fuel from 3 different sources: the OEM electric "lift" pump, the fuel pressure regulator (FPR), and the integrated 1-way valve.
Note that the BMW fuel pump is still retained but is now repurposed as a "lift" pump to fill and maintain volume in the FHST. The lift pump fills the FHST canister through a special orifice in the FHST. This keeps the required pressure for the venturi jet pump(s) to be active and delivers fuel to the lift pump. When a low demand for fuel is present, the FHST canister will overflow back into the LH side of the OEM tank. Fuel will then cycle back into the FHST through a 1-way valve integrated into the bottom of the FHST. Unlike traditional surge tanks that rely heavily on surge tank pumps and lift pump flow matching, the FHST uses an extra source that negates this important relationship. No matter what is dynamically changing with the other 2 fuel sources, the high-flowing 1-way valve will constantly supply fuel to the FHST canister until the LH side of the gas tank becomes extremely low. At this point, it is up to the lift pump and the FPR to supply the last few ounces of fuel to the FHST.
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Integrated Fuel Pressure Regulator
Like OEM, a fuel pressure regulator (FPR) is integrated into the unit. Furthermore, if an intake manifold signal is installed, this FPR can operate at a 1:1 ratio permitting fuel pressure to proportionally increase with boost pressure. The returning low-pressure fuel from the FPR is sent back into the FST canister keeping it full. A 6-hole diverter evenly disperses fuel inside the canister preventing air bubbles and foaming. Also, 2 fuel return orifices are included for fine-tuning the desired fuel pressure to the fuel pumps' flow rate.
New for Radium Engineering P/N: 20-0970 and 20-0972 is an option to install an external fuel pressure regulator.
The optional 20-0806 Fuel Hanger FPR Block-Off (described below) is necessary to bypass the integrated fuel pressure regulator, as shown above.
