Is it the fact that a race header has no cat why they are so loud? If so would adding a high flow cat reduce the noise? Also, how would this effect horsepower? If a cat won't quiet it how will adding another resonator effect the horsepower increase?
well basically yes. YOu would have to weld in a cat/resonator into the setup somewhere. Best place would be in the catback setup. There's a long straight pipe (At least on my Borla) that could be cut and have something welded in there to quiet the noise..