[thstone]

With two O2 sensor ports on each side, this header might be able to pass the smog test fairly easily because the computer will be able to adjust the air/fuel mix to minimize emissions.You'll need all four O2 sensors (pre and post cat) for the ECU to tune the air/fuel mix properly to pass the emissions test. If you get rid of the post-cat O2 sensors, the engine will run fine but the emissions might fail the test.

If you do this, be sure to drive the around for 20-40 miles in varying conditions to get the ECU to fully adjust for the header change.

Its unlikely that the test tech is going to get under the car to do an actual visual inspection of the headers and even less likely that he'd know what he's looking at.

With all of that being said, you'll have to check with the header manufacturer to find out if their product is CA approved. If not, then its technically illegal but you still might be able to pass the smog test.