I heard I would lose back pressure by straight piping but I would like to know if there would be any further problems with my turbo. Would it run the same? If I were to put stock back on it would it run normally again? Anybody got an answer?
Changing the cat back portion of the exhaust is not likely to impact performance, you are not likely to hurt anything. Will it sound good? If I had to guess, probably not.
The less back pressure the better in turbo applications. It would not be a problem at all. If you want full straight pipe all the way back you'll need to look into a catless downpipe. Our catalytic converters are built into the downpipe, which is a pretty complex piece. And of course going catless will probably throw a CEL, even with defoulers. There are conflicting reports on the defoulers and CEL, some get it right away, some after a few dozen miles, and then there are some who report no CEL. As for how the engine runs, I don't believe you'd need any kind of tuning to adjust for anything, as everything that can be tuned happens before the turbo, therefore it should run just like stock, swapping between the two exhausts shouldn't have any effect.