a friend whos shop is going to re do my drag piping told me the same thing, that cause i have 2inch off the turbo and 2.5 going into the motor that i should upgrade, they said that alli would have to do is go a little more with thte boost to compensate for the larger pipe but i would be able to move more air velocity, at a better rate, i thought that the bottle neck theory would be better and go from larger to smaller but im not the turbo guru i guess