I am putting together a custom exhaust setup and figured someone would chime in with the answer to this question quicker than I could jack the evo up and measure!

What size flange will I need to make the connection to the stock down-pipe? Is it 2.5in? I would just cut the flange off the cat and weld it to my piping, but I wouldn't mind making this setup easily interchangable back to stock because I haven't kept a car for more than 6 months for several years now and its next owner may not care for this exhaust setup! haha

Thanks in advance. Hopefully it's not a stupid question. I did a quick search but didn't come up with a definate, clear answer.