I'd say yes it will change the preformance, by how much I'm unsure. Any extra pipe work cause more drag at the same air velocity. Plus It almost like a bottle neck, or reducer before the turbo. But if it make it run, and is a vital part of the setup, I'd fit it and see how it runs. I'd also say vapor blasting may be not aggressive enough to smooth out the metal on the inside. Media blasting would be best bet. Or buy a cheap sand blast gun if you have a compressor and use cheap BnQ or wickes sand. And give it a good hot wash afterwards.