I have the NW downpipes going to the OEM exhaust. So no cats. Stock muffler and resonator. Sounds good, not too loud, no drone. I only notice the fuel smell at start up. After that I can't smell a difference. The downpipes really changed the power delivery. From low end grunty power to a more top end hit. The loss of low end power makes the car not as fun I think. I had a dyno tune after installing them and made 366 rwhp. I might try swapping back to see what's better for me.