I have a 2000 si w/a d16y7 in it. Some have told me that the catalytic should be on the exhaust manifold. My car has an aftermarket 4/2/1 header on it. There is a test pipe on there now but I have an oem cat coming in for it. Why am i being told that the catalytic should be on the manifold? I can see the cut secondary o2 sensor wires right above where the test pipe is. Can someone please clear this up for me?