My budyy has a stock o2 housing 3" cat-less downpipe and the Ebay 3" cat-back exhaust "DC Sports knockoff". His left exhaust tip is perfectly clean, I mean as clean as if you just washed it. His right side "passenger" exhaust tip has carbon on the inside indicating that the exhaust is exiting that pipe. When he turns the car on you can feel exhaust coming from both tips, but not much from the drivers side tip. Any idea as to why it would be doing this and do you think his exhaust is hindering his performance? He said, he really didn't notice a BIG difference if really any when he got his exhaust put on. He only has a WGA and intercooler for his other mods. Just curious about this.