Roger Clark Motorsport Parallel Fuel Rail Kit w/SX RegulatorParallel fuel lines are a great addition to any engine, not only do they provide a more consistent volume of fuel to your injectors but they also yield key safety benefits. With Subaru's standard fuel system design, fuel is fed by a pump from the tank to the front of your car passing through the fuel filter (located in the engine bay) before being fed into the fuel rails. Fuel is then delivered to each cylinder one by one, starting with cylinder four.