[integralover]

it would be best if you are going to replace the pistons to replace everything down there. you don't have to but it is best. now depending on what you plan on doing ie. turbo, supercharger, nos. you will be seeing higher HP gains and stronger internals would be better. will make the engine more reliable. as with the fuel, with new injectors, and i'm assuming that you are getting bigger injectors, you should go ahead and upgrade the fuel rail and pressure regulator and fuel pump. you will see a small HP gain from the fuel upgrade but not much. doing a fuel upgrade is better for the engine when you do forced induction or a NOS application. that is where you will see noticable gains.