I didn't read or claim to read anything about the sound, I just stated that you might end up with something that sounded like a ricer with a fart can. But I did do a search on Yahoo by typing in "average horsepower gains from headers" and a few other similar phrases. The results I came up with from a few sites stated with just going from a manifold to a header would gain 7 to 20 HP. But the sites with actual results with just headers alone was showing 7 to 8 HP gains. Some were showing more, but they were trying to sell headers . The sites that showed actual gains were performance & racing shops.