Hi, I've searched around and found many reviews concerning exhaust setups but none of them relate to smogging.

Can anyone tell me what fails smog and what passes.

From what I can gather, test pipes do not pass.
What about Y pipes, H pipes and all the exhausts?
Do headers cause smogging to fail too?

 

Here is the bottom line for CARB ("legal") approved parts.

http://www.arb.ca.gov/msprog/aftermk...es/amquery.php

If you don't see the part here, then it isn't legal in Cali. Exhaust may be an exception, not sure. But I do know that headers need to be CARB approved to be legal in CA.