I also have the corsa track systtem. I am thinking about having the stock primary cats removed. But their was a very interesting thread by Final GTS on 10/9/06. #598981
This was very interesting info about which stock cat to remove. Just a post on that thread.
"As many of you know, and some don't, the SRT comes with 4 Catalytic Converters. The two upstream are Ceramic Substrate, and the two downstream are Metallic Substrate. Let me say that again; The two downstream are METALLIC SUBSTRATE..... The STOCK CATS are actually a 5" diameter substrate, while the RT cats are only 4"! What does that translate to? That means the STOCK CATS have 160% of the Cell-Surface area of the RT cats! Before some of you knowledgeable people call it, yes, the CPI (Cells Per Inch) is the SAME as RT. The key to getting the flow out of the stock cats is the size piping used with them, and cutting down the number from 4 to 2. The primarys are high flow, too, but from what I have seen, they start to come apart FAST. my pair was already showing signs of cell fracture at 12000 miles, with various cells plugged as a result. Not nearly enough to cause a problem- but you could bet your bottom dollar by 25000 miles it would cost you some power if the rate remained the same.
Well, thats just the parts. Getting it into the car is a whole 'nother ball game. Unfortunately, at this time, there does not appear to be any way to even get the parts to do this unless you have a set of RT cats first... as the correct 3" pipe, lip, bend, and hangers are all part of their setup. However, for someone who ever has a set fail, this is certainly the way to go: "