My car has a single muffler. I was wanting to put in an exhaust system. I was wondering if I put two mufflers, would I have to change the stock headers to see gains in performance? If I don't and I didn't change stock headers would I gain performance benefit of two mufflers or will the only change be the sound. I think it may not gain performance since the smoke is channeled directly through headers (with a diameter of whatever stock is) out through the end. Widening the diameter of the headers would facilitate the engine's output. So in order to see gains in performance do I have to change headers.