A low-pressure fuel pump (which varies from ~40-95psi) delivers fuel from the gas tank to the engine. Then in order to spray fuel directly into the combustion chamber, a high-pressure camshaft-driven pump pressurizes the fuel to upwards of 130bar (almost 1900psi !). Unfortunately on cars that have many modifications, the stock fuel pump cannot flow enough volume of fuel to maintain the system pressure and the car gets the familiar “fuel cut” that so many modified customers experience.
Because of this dependency on engine rpm for the high-pressure fuel pump output volume, the FSI pump is capable of flowing almost 370hp at 7000 rpm but yet only 158hp at 3000rpm. The only way to address this issue while maintaining a pump that fits in the stock location is to change the volume of the pump’s internal pressurization chamber.