I'm working onmy buddies '96 4dr lx civic, and it has a crack in the header. It goes from the O2 sensor toward to block. My real question is the cat converter seems to be part of the exhaust manifold, is there a performance header I can put on, or will I have to add a cat converter down stream if I put a 4-2-1 header?

 

you ahve to add a cat if you get a header.

 

You need an EX cat and either cut your existing midpipe, or run an EX exhaust.