Power probably isn't going to increase no matter what muffler you put on. But loudness and sound can be achieved in different ways. I have a mac 2 into 1 exhaust on my bike and it's louder than stock but not as loud as a harley. Others have used harley mufflers or straight pipes. If you have nice mufflers on your bike don't screw with them. Just get new/different ones. Harley dyna or sportster mufflers should be had for about $30 a pair on ebay. Don't pay high prices.