I am starting this post because I am fed up with the rubbish I read in different forums regarding certain performance tuning measures. I will develop this thread slowly as it is a lot of work and will try to keep it to Fiats, but most of it will be applicable to other brands as well. It all started with a fuel pressure regulator. Some ruthless sellers of performance items (I am not calling them performance tuners as the are at best performance bodgers) try to sell fuel pressure regulators as the best thing since sliced bread. What is the purpose of a fuel pressure regulator? Either to keep the pressure constant or to regulate the pressure to cetain values the ECU can reference to. So, why then doesn't do the fuel pump this? Because the purpose of the pump is to supply fuel. The fuel pump is operating at a set pressure, but when plenty of fuel is needed all of a sudden or the engine changes rapidly to low rpm then pressure fluctuations come in that upset the fuel delivery and in due course the ECU has to even out this on top what it is supposed to do. There is some reasons for the need to stabilise or regulate the pressure. Also it needs to be remembered that even if the ECU can adjust to fluctuations the lambda sensor sits several strokes behind, which means it is running late after the values and then telling the ECU to intervene. To supply the amount of fuel needed in the combustion chamber the ECU relies in the basic program on a set fuel pressure, a set injector size, a fuel pump that delivers a certain amount of fuel and the variable injection duty cycle. As most cars run with duty cycles of 60% a good 50% power increase is possible before uprating any of the components for fuel delivery. Even the best AIRs will not increase peak power by more than 13%, which is just about the capability of the ECU to adjust the fueling for (the ECU is purposely limited) the extra air. Fitting a fuel pressure regulator for this is outright nonsense. This calls only for a re-map to get the best out of the engine. A fuel pressure regulator does not increase fuel flow as much as people think. If you have a system pressure set at 3.5 bar the increase to 4 bar would only increase the fuel delivery by 7%. Going from 3.5 bar to 5 bar would increase the fuel delivery by 20%. But this is the theory because the fuel pump will not support it to this high a pressure. Also it has to be remebered that a lot of the fuel sender units have the pressure regulator in the unit built in. This would require removing the regulator from the tank and altering the sender unit. TBC.