When injectors are upgraded, the fuel pressure controlled by a factory fuel regulator may become too low, and injectors' atomization performance may be deteriorated. To improve such conditions, HKS Fuel Regulator can adjust the fuel pressure appropriate to injectors' capacity. Also, HKS Fuel Regulator can increase the fuel pressure without replacing injectors to increase the amount flow. (Extreme initial pressure change may cause bad atomization. Also, it increases the load to the fuel pump; in this case, the fuel pump may have to be replaced.) Uses -6AN Fittings.