Clogged cat can cause it to idle/run like shit but your problems seem to be motor related (hurt motor), re-ring and see how it goes.
no cat. the D16Y7 had a cat/header combo, so anyone who puts in another motor leaves the cat off. i have a 4-2-1 header into the mid-pipe into the muffler section.
i was just wondering if the exceeding restrictiveness could have something to do with it running poorly. im looking for another exhaust currently...