OK, here's what this exhaust shop told me. Being an N/A u still need some back pressure, if the exhaust system is too big, then it will overkill. Old stuff. So I ask what happen if i still want to use my free-flow muffler? is 2.25' too big? He said I will better off with 2' if i still want to keep my free-flowing muffler. If I want 2.25 the muffler gotta go and swap into reverse type. No need for hi flow cat too, this is what the other exh shop told me aswell. As for headers, well that is damn hard to find but on Monday, hopefully, the exh shop can find me Hurricane headers. Another thing the exhaust shop told me, mandrel bent is not needed if you're only getting 2' to 2.25'. For turbo, you will want to opt for mandrel bent. Another idea I had in mind is to copy Sportivo exh system size. But I knew 2.25' is a bit too big for 1.8 engine.