The underdrive pully kit's pullies are all supposed to be much lighter than the factory pullies which means less weight for the engine to have to turn which means more power. I don't remember the science behind the undersizing of the pullies themselves but that is also supposed to help. It's not gonna be like reprogramming the ECU but it should produce close to the same amount of gain as a throttle body spacer. Just enough to notice a difference. I know in the 4 banger crowd, lightweight/underdrive pullies are a good mod because it frees up quite a bit of power. Ofcourse freeing up 5hp in a 02 Mitsubish Lancer is freeing up a lot of power, . Couldn't hurt to try it. You are running out of bolt on modifications left to do you know.