What is an FMU?
An Fuel Management Unit (FMU) is a special rising rate fuel pressure regulator placed in the fuel return line of the fuel injection system. This is a very common approach to handling the increased fuel demand required by supercharger kits. It does work. It will make the injectors flow more fuel than their rating. These are used in addition to the factory fuel pressure regulator and only have an affect under boost. They are rated by the ratio of fuel pressure to boost pressure. For instance, a 10:1 FMU will give you 100psi fuel pressure at 10 psi boost pressure. The problem here is that the extra pressure on the fuel pump decreases the flow capacity of the pump. That is the last thing you need on a supercharged engine. You can offset that by installing an in-line fuel pump in addition to the in-tank pump.
