Ok I was going to have a catless 2.5in downpipe for my turbo setup, but the question is, would I have to tune the computer for it or can I just leave it? Im going turbo so I am not getting headers. And I have a 2.5in turbo downpipe already so I am going 2.5in. But I am also asking out of the random blue, what is so much better with a 3in over 2.5in.? Thanks for the help.