i've heard that the 2.2 ecotec header from dc sports is compatible with the lsj, and that it is small and restrictive. but it DOES fit. meaning that the flanges are all the same. right?
so, my question is, is the rest of the exhaust the same? for example.. if i got a 2.5 inch catback for the 2.4 litre ss would that work? i think 2.5 inches is big enough right?

 

Yes you are golden with a 2.5" exhaust.

If you are upgrading to an aftermarket header. I suggest you get a new downpipe with a high flow CAT as well.

I would reccomend the Cobalt-Addiction 2.5" downpipe w/high flow CAT.