Modification of the 2.0T FSI engine far beyond OEM power levels requires an additional volume of high-pressure fuel especially in the midrange (3000-5000rpm) of the powerband. To understand why this fuel is needed for the midrange, one must first understand how the fuel delivery system works in the 2.0T FSI.
A low pressure fuel pump, which varies from ~40-95psi, delivers fuel from the gas tank to the high pressure fuel pump. Then the high pressure, camshaft driven pump pressurizes the fuel to upwards of 130bar (almost 1900psi!) in order to spray fuel directly into the combustion chamber. 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 suffers from the familiar "fuel cut" that so many modified customers experience.