2004-2006 Subaru Impreza WRX STi / 2005-2006 Legacy GT / 2004-2005 Forester XT

The PERRIN Performance fuel rails represent a true advancement in boxer engine fuel delivery. The PERRIN Performance fuel rail kit is not just a replacement part. They have completely redesigned and redirected the fuel from the supply lines to the injectors, thus solving all fuel distribution problems insuring even fuel distribution to both banks of cylinders on the boxer engine. As clients continue to expand the HP in their vehicles, the need for even fuel delivery is more critical. Failure to address this concern and could result in your expensive motor quickly needing some major attention.

Perrin's newest variant of this rail system is both easier to install and safer than ever before. To further prove Perrin's distinction as the industry leader in fuel rail technology for Subaru applications, they now include DOT approved fuel lines and PERRIN Pyroshield! This fire retardant sleeve is placed over the fuel hose to protect the fuel lines from being subjected to extreme under hood heat created by high horsepower turbocharged monsters. This lowers the fuel temps, thus improving horsepower and increasing longevity. These fuel rails come in BLACK with aluminum PERRIN logo plates to suit any engine bay.

How a Fuel System Works
The fuel system consists of 6 main parts: Fuel tank, pump, Fuel lines, Fuel Rails/distribution blocks, injectors, and pressure regulator. All these parts work together to keep the fuel injectors supplied with fuel and at a steady pressure. All of which are important to making a fuel system function properly. The fuel tank holds the fuel, the fuel pump picks up and delivers fuel to the fuel lines. The lines transfer fuel from the pump to the fuel rails, and the pump keeps continuous pressure behind the fuel injectors. The regulator controls pressure by bleeding off pressure/fuel to another fuel line dumping back into the tank, where the cycle starts all over again.

The most important part of this system are the fuel injectors. Ultimately these are what are delivering the fuel. But all the systems in front of them have to function properly in order for fuel to be delivered accurately. In order for the fuel injectors to work, they need fuel behind them and this fuel needs to be under a given pressure. As the injector opens up the pressure and fuel behind the injector allows for the fuel to be sprayed out in a fine mist. When the injector fires, fuel pressure drops slightly as the fuel pump tries to keep up. This pressure drop carries across the entire fuel system and affects all the other injectors.

Because the OEM rails are not designed to deliver fuel equally to each injector, this pressure drop doesnt affect all injectors the same. Some will have less pressure than others, and in turn not deliver equal amounts of fuel to the cylinders. The effect is not all cylinders run at the same Air Fuel Ratio (AFR), which effects the ultimate power to be had. Imagine this happening at high RPM, and high load where injectors are firing lots of fuel and firing very quickly. Bad things can happen.

The 2 factors that play into this unequal fuel delivery are the OEM fuel lines being very small, and that the OEM rails are not routed to deliver fuel equally to each injector. The cure is installing PERRIN High Flow fuel rails.

So why does the OEM build them this way? Because it is cheaper, and for the stock power level, they work fine, but if your reading this, your not building a stock car.