Originally Posted by nigt4003

I still have my stock cats with roughly 50k miles on them but I swapped those out for Berk Resonated HFCs a year ago and now running ISR Resonated Test pipes since KS doesn't do emissions tests. (Thank goodness!)

Long story short, I did a tune while I had HFCs on that ran stupid rich and actually burned out the cat to the point it sounded like rocks and I was misfiring badly at highway speeds. Since the test pipes I've been good and don't have to worry about any blockage issues anymore since there aren't any! If you're wanting to go the semi-loud route I'd suggest test pipes and a muffler but obviously CARB compliance is another factor into that decision.