I've got a B16A with a DC 421 Header with no O2 bung does anyone know what size collector they use? It is a 2"? and does it matter what size the inlet is on the cat? I want to replace the test pipe an go emissions legit since I have to pay extra to someone to pass emissions anyway. The test pipe is 17" long and I don't know what the I.D. is on it. I know I have to get a cat with an o2 bung in the front that is 17" that exits to a 2.5" exhaust. But I don't know what size the inlet needs to be as the outlet I was going to match the rest of the exhaust at 2.5". ANybody know?