The AAM Competition Fuel Rail System is a direct replacement and upgrade to the factory fuel system. The factory fuel system is a "return less" style system. A “return less” style system offers minimal adjustment to the amount of fuel the engine can receive. This can work well in a factory naturally aspirated setup, but has several draw backs when you go to forced induction. One negative aspect of the factory returnless system is that the factory fuel pressure regulator is installed in the fuel tank. The factory fuel pressure regulator does not allow fuel pressure adjustments and is incapable of holding a constant fuel pressure with most aftermarket fuel pumps. The factory fuel pressure regulator also is unable to add fuel pressure under boost. Most factory turbocharged setups use a “return style” fuel system. In a “return style” fuel system the fuel is feed from the fuel pump to a fuel filter, then to the fuel rails (which feed the injectors), and a fuel pressure regulator regulates the fuel after the fuel rails to keep a constant pressure. This systems allows a 1:1 fuel pressure regulator to be used, which will typically increase the fuel pressure one pound for every pound of positive pressure (psi/boost) a turbocharger or supercharger is pressurizing your vehicle. This system can also use an adjustable fuel pressure regulator which greatly aids tuning on the dyno.