When increasing engine output by increasing the engine bore or revolutions, changing turbo or boosting up, finding the most suitable fuel-air ratio means setting up the injectors to provide the correct injection condition to meet both the increased volume of air and the max volume of fuel to be introduced by the injectors. Combustion-related tuning involves control of the fuel pressure regulator, which in turn controls the pressure of the fuel being provided by the fuel pump, as well as the electronic control module (ECM) which controls the injectors which actually spray the fuel into the engine. All of these must be in balance.

By changing to a high-flow fuel injector, the amount of fuel that can be provided during a given time increases. If only the injectors are changed and the ECM left in its original state, the tendency is for too much fuel to be provided. If only the ECM settings are changed, the amount of fuel the fuel pump provides to the injectors will not keep up with the demand in high rpm range, resulting in insufficient fuel supply and a fall in pressure.

By changing to a high-flow fuel pump, more fuel can be provided to the injectors during a given period of time. If it provides more fuel than the injector can spray into the engine, fuel tends to back up and the pressure rises.

Fuel is drawn from the fuel tank and fed to the collector tank.

In order for fuel to be well filtered but efficiently supplied with low pressure loss, the filter should be changed to a high-volume type.

To keep the pressure of fuel provided at the optimal level, this has a valve which returns fuel that was not used by the injector via a return line to the tank. The pressure of the valve is controlled by a spring and vacuum pressure (the pressure in the surge tank). The NISMO fuel pressure regulator can be adjusted to vary the fuel pressure by turning an adjustment screw to change the spring load. When fuel pressure is too low, the injector does not provide good misting of the fuel; if too high, it can result in the injector valve not closing completely.

By temporarily holding fuel already drawn from the fuel tank, the influence of the fuel volume, pressure and temperature within the fuel tank is eliminated, and a stable fuel supply is provided to the injectors.

If some pressure remains in the line after the engine is shut off, engine restart is improved.

Controls instability of fuel flow within the fuel line, insuring stable fuel pressure.