whats an fpr and why wopuld i need one?
Its a 4 bar Fuel Pressure Regulator (Standard is 3 bar), Mainly used when a k03s has been fitted (and I assume when bigger turbos have been fitted along with injectors), to increase fuel rail pressure. So when the injectors are pulsed open by the ecu more fuel can be injected in the time its open than a standard 3 bar fpr due to the higher fuel pressure. If you get what I mean.
IIRC its a cheap way of getting more fuel into the combustion process for more power, needs mapping to make full use of it, as on a standard car the Ecu would recognise the engine is running rich (due to it not having enough air to burn the fuel) and adjust fuelling to bring mixture back into limits.