INTRODUCTION
For many years Radium Engineering has been touting the benefits of a fuel pulse damper (FPD) in fuel injected systems. Formerly only seen on OEM fuel systems, Radium Engineering was the first to introduce the FPD to the high-performance aftermarket in 2015. OEM-grade fuel pulse dampers are specifically designed for the factory fuel system parameters. When modifications are made to the fuel pump, fuel rails, injectors, etc. these dampers are no longer as effective, or they must be removed for modifications to be carried out. Radium Engineering fuel pulse dampers are designed for use with high performance fuel systems, so damper benefits can still be realized.
Radium's most popular 8AN ORB direct mount FPD-R
DAMPER SOLUTIONS IN THE OEM
Most OEMs will utilize some method to attenuate pressure pulsations. Manufacturers prefer to avoid adding cost to a vehicle so in some cases you may find some other methods employed to attenuate the noise, instead of a pulse damper. These methods include rectangular cross-section fuel rails with a carefully tuned width and height, strategic location of the fuel pressure regulator, fuel lines mounted to the body using vibration isolating mounts, etc. For some OEMs the noise is not an issue and there are no negative effects on fuel delivery, so no measure is taken to address fuel pulsations. It is different from application to application.
Internal components of an OEM pulse damper
A fuel pulse damper on an OEM fuel rail
WHAT DOES A PULSE DAMPER DO?
An FPD is used in fuel injection systems to attenuate (absorb) pressure pulsations generated by the fuel pump and by the injectors opening/closing. These hydraulic pulses can cause an undesirable noise, which can be transmitted to the passenger compartment. Under certain circumstances, they can even cause issues with fuel delivery to the engine. These pulsations can sometimes be large enough to hear and feel, but most often are undetectable with a liquid-filled analog mechanical fuel pressure gauge because they happen so quickly. To truly see fuel system pulses, fuel pressure data logging must be done with a high-quality fuel pressure sensor and a sample rate of approximately 500Hz.
The fuel pulse damper works by allowing the volume of the fuel system to change slightly to absorb the pulses. This is done with a spring-loaded flexible diaphragm inside the damper.
Fuel pressure fluctuations on a 4-cylinder engine
with and without a Radium fuel pulse damper installed.
How do I know if I need a Pulse Damper?
As mentioned earlier, fuel system pulsations can have an undesirable effect on cabin NVH (noise vibration and harshness) by causing knocking sounds in fuel lines. They can also contribute to uneven fuel delivery and mysterious lean spots that are difficult to tune out. These are often the result of the hydraulic pulses acting in harmonic resonance with the injectors opening and closing. This issue can be aggravated by high-flowing aftermarket injectors. In some vehicles, these lean spots can result in stumbling during acceleration, commonly occurring in the 3k-5k RPM range. If you are experiencing any of these issues, a damper could be a good solution. A fuel system that is plumbed with mostly hard metal tubing will be more susceptible to knocking and pulse issues than a system made with flexible rubber fuel hose.
Pulsations are not JUST about the noise. Most EFI tuners are not concerned with the noise, but rather with engine performance and seek constant, reliable fuel delivery throughout the RPM range in order to optimize the EFI tuning. If everything is running great, and fuel delivery is spot-on and there is no fuel line knocking noises, then a damper would not provide any benefit to the system.
A damper IS NOT a magical "cure-all" for any fuel system problem or tuning issue!
Example of a hard line fuel system that may be prone to audible knocking
WHICH DAMPER DO I NEED?
There are 3 considerations and decisions to make when selecting a fuel pulse damper:
- Operating Range
- Direct Mount vs Inline
- Connection Type/Threads
Operating Range
Radium Dampers come in a standard range that operates from 40psi to 70psi, and an extended range that operates from 40psi to 105psi. The selection of operating range can be made based on static/base fuel pressure. Since vacuum ports are integrated to allow a 1:1 rising/falling rate of the spring, you can choose strictly based on the base pressure.
Direct Mount or Inline
Direct mount dampers are available in 3/8" NPT and in 8AN ORB male threads. These are designed to mount directly to ports in the fuel system that have female threads to match.
Note: All Radium fuel rails use 8AN ORB threaded ports.
Inline dampers can be mounted remotely and fuel lines run through them. These should be used when there is no location on a fuel rail or other device to direct mount a damper.
Connection Type/Threads
Direct mount dampers are available in 8AN ORB male threads, or 3/8" NPT male threads.
Inline dampers feature two ports threaded 8AN ORB female, so any 8AN ORB fitting to adapt to numerous fuel line sizes and connection types can be used. Many early releases of inline kits come pre-packaged with barb fittings or AN fittings.
The green-top short (FPD-R) is perfect for static fuel pressures up to 70psi.
It also fits into small spaces.
The black-top tall (FPD-XR) is great for vehicles with higher static
fuel pressure, up to 105 psi.
Inline dampers can be outfitted with many different styles of fittings.
WHERE DO I INSTALL MY DAMPER?
It is preferred to mount a damper as close to the source of the pulsations as possible. This usually means mounting a damper directly on the fuel rail. If your fuel rail has an available female 8AN ORB or 3/8 NPT port, then you can use a direct mount damper, FOUND HERE. What is an ORB port? CLICK HERE
If the fuel rail does NOT have a compatible port, then an in-line damper should be used, FOUND HERE. The inline damper should be located on the fuel feed line, within the vicinity of the fuel rail, but exact placement is not critical.
If an engine has two fuel rails (V8, V6, H4, etc) it is not always necessary to install a damper on each rail. However, testing will have to be done to verify. In most cases a single damper is sufficient.
Radium Direct-Mount pulse dampers mounted on fuel rails
CAN I USE ADAPTER FITTINGS TO INSTALL MY DAMPER?
If a fuel rail does not have a compatible port, adapter fittings can be used without sacrificing the function of the pulse damper. Note that Radium Engineering offers fuel rails for all popular engines (and even some unpopular ones!) that have ports for an FPD.
HOW MANY DAMPERS DO I NEED?
In most cases, just one. However, special cases may require more. This will take experimenting, as each fuel system is different and pulse damping is complex and not intuitive. For example, OEMs may place a damper near the fuel pump outlet, multiple on the fuel rail(s), and even on the return line in order to make sure that the system is as pulse-free as possible. This is not entirely necessary on a modified high-performance vehicle, as the needs of a performance car are different than a mass produced passenger car.
If an engine has two fuel rails (V8, V6, H4, etc) it is not always necessary to install a damper on each rail. However, testing will have to be done to verify. In most cases a single damper is sufficient.
DO I NEED TO HOOK UP THE VACUUM PORT ON MY DAMPER?
The vacuum reference port on the damper should ONLY be hooked up to the intake manifold if the fuel pressure regularly exceeds the maximum pressure for the damper. This is 70psi for the FPD-R and 105psi for the FPD-XR. This can happen on boosted vehicles with 1:1 rising rate pressure regulator.
If fuel pressure does not exceed the upper range values, then a vacuum reference is not needed and the port on the damper can be plugged with the included screw.
Reference the FPD install instructions for more details.
