What do they do for you? Are they really beneficial? Is there a noticable difference with pulleys or cam gears?

 

Well you already have a fuel pressure regulator stock. I think you're refering to an adjustable FPR. This allows you to increase the fuel pressure causing the injectors to shoot more fuel. Not really usefull unless you're running lean. These are often added after numerous mods to increase air flow through the engine to add an equivilent amount of fuel.

 

THanks