Here's some more info than what I had PM'd you (just so everyone else can chime in or get the info) :
1.) It will fit, but its a little tight and I would use the gasket that comes with the header
2.) Since the pre-cat was in the OE manifold you will pop a p0420
a.) Can fix with a spark plug fouler mod, but it blows not recommended at all
b.) You can get an 02 sim which will fix the problem, but its pretty shady legally
c.) You can extend the 02 harness and install another cat welding in a bung after it
3.) Down pipe would be for a turbo install (post Turbo)
4.) If your thinking of a mid pipe I didn't look into it, but our exhaust config is a little off from the TC or XB so you might not have very good luck.
If you are worried about emission there are 2 kinds of testing OBD-II reading to check that you have no codes even ones that won't always pop a CEL. And then there'e the dreaded sniffer that will actually measure your exhaust gas output levels. I didn't have emissions testing in my area so I didn't really care, but if you do I wouldn't really worry about a header unless your prepared to get it sniffed and then see if you need to get another CAT etc. If you do go with a header and you have to get smoged make sure you run it like a bat outa hell (no chip/tune/etc. stock ECU strategy) for a few miles to get the remaining post cat heated up. That may allow you to pass your emissions depending on the state requirement.
2009 Silver Vibe GT AutomaticI/H/E/Unichip @ 93octaneMy Garage : http://forums.genvibe.com/zerothread?id=43521
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