A bit silly question, would fitting 3.5 or 4bar fuel pressure regulator on a stock agg give more top end grunt or just do more harm than good?
all it will do is make the car run like arse. the injectors will put more fuel in than the ecu intends, and it'll have to dial back to try and compensate. If the ecu was remapped to match, you would be back to where you started. although if the remap was done really well you will gain a bit, but you would also have the same gains if you remapped with the stock fpr. the only time bigger injectors and/or fpr is required is when you do some serious mods to the engine, enough that the stock setup can no longer supply enough fuel. but the stock setup has plenty of overhead so its unlikely you'll need to worry put your money into an abf engine instead or something better, you'll see way more benefit for your money
