Radium Engineering Fuel Pulse Damper Direct Mount Kits FPD R or FPD Radium Engineering Fuel Rail In Line Extra Range Pulse Damper 6AN Radium Engineering Fuel Pulse Damper Direct Mount Kits FPD R or FPD Evasive Motorsports: Radium Engineering Fuel Pulse Damper Extra Range Radium Engineering Fuel Rail Top Port Fuel Pulse Damper 8AN ORB Swivel Radium Engineering Fuel Pulse Damper Direct Mount Kits FPD R or FPD. The opening and closing of fuel injectors creates pressure pulses in the fuel rail which can lead to unstable fuel pressure. In order to achieve a safe and consistent rail pressure, a fuel pulse damper (FPD) is often necessary. The FPD's internal diaphragm will absorb oscillating pulses and stabilize fuel pressure. This correction can be measured throughout the RPM range and can often help idle surge, especially with high flow injectors. Furthermore, a fuel pulse damper can help solve erratic lean air fuel ratio spikes, commonly experienced as "stumbling", that are difficult to tune out. What makes Radium FPDs unique? Along with having the flexibilty of using common fittings, Radium Engineering FPD's use a vacuum boost reference port which allows for proper fuel pulse damper performance even at elevated fuel pressures. This becomes essential for boosted systems that use a 1: 1 rising rate fuel pressure regulator. WHICH DAMPER DO I CHOOSE? The FPD R (Fuel Pulse Damper Range) and FPD XR (Fuel Pulse Damper Extra Range) both have unique base "static" fuel pressure requirements: FPD R base pressure requirement = 40 70psi (static) FPD XR base pressure requirement = 40 120psi (static) Base pressure is the fuel pressure measured when the fuel pump is running WITHOUT a vacuum line connected to the regulator. IMPORTANT: The ranges above are base static fuel pressures only. Any dynamic fuel pressure created by a rising rate FPR outside of this range is acceptable, but only when the base "static" fuel pressure is set within these ranges and the vacuum boost reference line is connected. Example 1: Vehicle: Mitsubishi EVO OEM Base Static Fuel Pressure: 43. 5psi Boost Pressure: 30psi Rising Rate Pressure Regulator? Yes Can I use a FPD R? Yes. Even though fuel pressure is 73. 5psi at full boost, the FPD R will work because the base static pressure was set within the 40 70psi requirement. However, the vacuum boost reference line must be installed. Can I use a FPD XR? Yes. Also, the vacuum boost reference line does not need to be installed since maximum fuel pressure does not exceed 120psi. Example 2: Vehicle: BMW E46 M3 OEM Base Static Fuel Pressure: 72. 5psi Boost Pressure: 20psi Rising Rate Pressure Regulator? Yes Can I use a FPD R? No. Base static fuel pressure exceeds the 40 70psi requirement. Can I use a FPD XR? Yes. Also, the vacuum boost reference line does not need to be installed since maximum fuel pressure does not exceed 120psi.