EFI fuel pressure regulators come in various shapes and sizes but all have the same purpose - to maintain a constant fuel pressure above the intake manifold pressure. The difference in pressure between the fuel rail and intake manifold or differential pressure across the injector should be maintained at a level to suit optimum injector operation.
The installation of an aftermarket fuel pressure regulator allows for the adjustment of fuel pressure to suit larger aftermarket injectors and other engine modifications. They are also necessary to regulate and flow increased volumes of fuel pumped by high flow aftermarket fuel pumps.
Fuel pressure regulator, which works with the fuel pump to maintain a steady pressure relationship between the fuel line side of the injectors and the intake manifold.
Most adjustable regulators are still one to one or close to that, however you can adjust the pressure at idle or full throttle for fine tuning. There is one other type of regulator that is used with aftermarket forced induction. These are rising rate regulators commonly called FMU's (fuel management unit). These regulators increase fuel pressure at a multiplication factor of boost. So instead of messing with complicated computers and injection duty cycles, these systems just increase fuel pressure to add fuel. They go inline down from the factory regulators and only start to add pressure under boost. So when you are off boost, you maintain factory tuning and drivability. Only as you get boost does the FMU begin to increase fuel pressure