i have searched on this and actually found LOTS of topics on this but none can answer my question........im getting ready to do an H22 swap on my SI and i plan on keeping the stock Jdm header with a stock H22 downpipe ....and as for the rest of the exhaust i am going to get a Megan test pipe along w/ Megan full 2.5 cat back........after searching i have found that the are differences in sizes....( the cat back narrows from 2.5 to 2.25 to the cat, then the test pipe i will be using has a 2.25 inlet and a 2.5 outlet)....and as for the stock h22 downpipe im not sure what the size of that collector is ......this soudns confusing but i am merely wondering if it will all bolt up with no problems.......stock H22 down pipe ----->Megan test pipe----->2.5 megan cat back....?

 

anyone?

 

the test pipe should have an oblong flange in order to bolt to the stock header. The collector on the stock header is smaller then 2.25 inches though, not really ideal, but it will bolt up.