well the stock cats are long gone.. both the GSR one and the stock D series one that actually came on the car. The reason I ask is because for about the same price, I can get either a new high flow cat OR the test pipe... Doesn't really matter too much either way to me... Like I said, for right now, it's stock with a bolt on here and there.. eventually I'm gonna be looking to boost it, but the whole thing needs to be rebuilt first. I'm in Athens, so we have no emissions.. that's not a concern. The high flow cat that I bought doesn't fit the header piping (too small) and the bolt holes don't line up. So basically I'd either be getting this test pipe or another high flow cat that does fit. Just looking for pros and cons to each.