I'm not so sure about that after reading the first post in this thread by goldentour. You are right in that the engine needs to be running properly but he stated his readings were worse after he installed a high flow cat. It would be interesting to see exactlty what those readings were. I would also be curious to see smog results from other duratecs with a list of mods, mileage, etc. This way we could all know if it is safe to use various combinations and still pass smog.
