It's fairly simple. It allows you to increase the fuel pressure on the injection system. Increacing the pressure will to some extent increace the fuel flow through the injectors. Usefull mainly on forced induction systems, ie turbos and superchargers. More fuel means more power: to some extent but with down sides. Unless the fuel is fully burned, you will end up washing the bores of the oil film, thereby increacing engine wear and destroying the oil. I would suggest that this is best used on a well tuned engine, when you know what you are doing with air flow, as well. Bear in mind that bolting on shiny bits without a propper tuning plan can result in a loss of performance! My philosophy for tuning is to start with getting the most out of the braking system, then the suspension and finaly improving the engine. You might be better spending the money on some good brakes and suspension bushes. Hope this is of help.
