Thought I'd pass this info on. I installed a set of Kooks long tube headers with high flow cats. And naturally the car started throwing post cat 02 codes. This is a common problem with high flows as they don't heat up as much as the stock cats and that's generally what causes the codes. Another issue is that the car should be retuned (preferably dyno tuned) as it will be running leaner with the new headers.

Once this is done the 02 codes will not return. If, on the otherhand, the car still throws 02 codes you can can always install 02 simulators. With these corrections done the car will pass emssions tests.