[b]What is a Fuel Pressure Regulator? [/b]
[i]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.[/i]
[b]Why and When do you need to install a Fuel Pressure Regulator?[/b]
[i]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
[b]Return Flow vs Base Pressure[/b]
[i]-Ideally a fuel pressure regulator will provide a constant pressure differential across the injectors. Base pressure has been defined as the difference between the fuel rail pressure and the manifold pressure. This is the actual pressure across the injector that affects the amount of fuel flowing through the injector when it is open.
-If the base pressure is constant this will aid in tuning by reducing the number of variables the tuner must account for.
-The fuel pressure regulator should have the same base pressure at a given setting for all return flow rates through the regulator.
-The return flow through a regulator can vary from maximum return flow at idle to approximately 25% of the return flow at full throttle and maximum rpm. For example the test RX7 would return 6L/min at idle and 1.5L/min at 7000 rpm full throttle.
-The base pressure is typically tuned at idle when the most fuel is being returned.
If large aftermarket pumps (or high volumes of fuel – eg alcohol based) are used this can mean the regulator is causing a restriction in flow at idle.
-This means that when the regulator is being tuned there is an increase is pressure due to the restriction in flow. This is caused by the regulator having to return too much fuel for its design. In effect the base pressure in then being set with a combination of spring pressure and pressure build up due to the flow.
-At higher load & rpm there is less fuel being returned through the regulator and the pressure increase due to the restriction in flow will be removed (as the regulator is designed to flow this flow rate) causing a drop in base pressure under these conditions.
-This drop is because without the restriction due to too much flow the regulator is only using spring pressure to regulate.
-Bench testing has also confirmed this relationship between regulated pressure and fuel flow.[/i]