Fuel Pulse Damper FPD-XR 8AN ORB Swivel Radium Engineering - USA-RAD-20-0777 - The opening and closing of fuel injectors creates pressure pulses in the fuel rail; this 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 is the difference between FPD-R and FPD-XR? The FPD-R is slightly shorter than the FPD-XR allowing it to be used in space-contrained applications. 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 - 105psi (static) Included -Anodized and laser engraved aluminum top, R=range or XR=extra range-Anodized aluminum body with male threads, 8AN ORB or 3/8" NPT-Stainless steel hardware-Rubber vacuum hose, 4mm ID-Vacuum hose Y-fitting  Instruction PDF