Radium Fpd-R, Inline, 6An

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  • Regular price $119.95

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. 

Most high performance OEM engines use an in-line fuel pulse damper from the factory including the Toyota 2JZ-GTE, Nissan VQ35DE, Subaru EJ20/EJ25, etc. The use of an inline damper is great for applications where there is not an option for direct fuel rail mounting.


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? 
At 1.98" tall, the FPD-R (green top) is slightly shorter than the 2.60" FPD-XR (black top) allowing it to be used in space-contrained applications. But the FPD-XR has a wider response range. Radium recommends to use the FPD-XR if you have the space.

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.

These dampers feature an anodized aluminum housing with a large 0.69" center bore. They use two in-line inlet/outlet ports machined with 3/4"-16 UNF threads for 8AN ORB fittingsDepending on the size of the fuel feed hose used, there are 3 kits to choose from which include different male adapter fittings (-6AN, -8AN, barb). These fittings seal to the billet housing using FKM O-rings.  

An 1/8" NPT female port is threaded into the center of the fuel pulse damper. A fuel pressure gauge is commonly used here or other sensors for pressure or temperature data.

Using the supplied M6 bolts/nuts, the FPD kit can be mounted at any possible angle including upside down. For best results, the damper should be plumbed as close to the fuel rail(s) as possible. Like any fuel system part, the FPD kit should be kept away from excessive heat areas. This product is safe for use with all fuel types including alcohol blends such as E85. 


The inline dampers are offered in three different versions and a selection should be made based on the type of hose connection needed.

-The -01 version is great for 5/16" (8mm) fuel hoses. Hose clamps required.
-The -06 version comes with adapter fittings for connecting -6AN hoses.
-The -08 version comes with adapter fittings for connecting -8AN hoses.

-Anodized aluminum top, R=range or XR=extra range
-Anodized aluminum body with female -8AN ORB ports
-Anodized aluminum ORB adapter fittings, selectable size
-Gasoline and alcohol (E85) resistant diaphragm
-Stainless steel M6x1mm mounting bolts/nuts
-Rubber vacuum hose, 4mm ID
-Vacuum hose Y-fitting 
-1/8" NPT plug