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.
Fuel pulse dampers can be mounted at any angle, including upside down. There are many variables that dictate if a fuel system requires fuel pulse dampers. For instance, there are cases where multiple dampers are necessary. There are also other times when the fuel system benefits with a fuel pulse damper on the return line.
NOT TO BE USED ON THE LOW PRESSURE SIDE OF MECHANICAL FUEL PUMPS (INCLUDING DIRECT INJECTION ENGINES).
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.
What is the difference between FPD-R and FPD-XR?
The FPD-R (green top) is slightly shorter than the FPD-XR (black top) 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)
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 105psi.
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 105psi.
Features
1. Male Fitting Selection:
a. The 8AN ORB versions seal using a FKM O-ring.
b. The 3/8" NPT variations seal with the tapered pipe threads.
2. Vacuum Port Orientation:
a. Because 20-0178 and 20-0179 use tapered threads (NPT), the vacuum port can be clocked to the desired location.
b. Even after tightened, the newest 8AN ORB dampers (20-0776 and 20-0777), will swivel permiting the vacuum port to be clocked 360 degrees. 20-0776 shown below.
3. This product is safe for use with all fuel types including alcohol blends such as E85.
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 
Part number 20-0776 shown above. Part number 20-0777 shown below.