The stock muffler is a dog. Sure, it keeps things quiet, but the engine's performance is crap. The B&B muffler will perform better, but don't expect a huge difference, and it will be louder.

I've got a G62 in my Yellow P47. A buddy of mine built an exhaust system which ran from the muffler through the firewall, exiting at the scale supercharger dump location on the lower side of the fuse. He used pipe that was just large enough to fit over the exhaust tubes of the muffler, and there were a couple of 90's and 45's in both stretches of exhaust. With all of this being said, I never thought my engine ran up the way it was supposed to. I'm running a 22X10 warbird prop. It ran good, just not great.

One day while flying, I realized that the engine was coming alive, as it was running better than ever before. The prop was actually starting to "bark". Upon landing, my buddy realized that the one exhaust pipe had come loose right at the muffler. Bingo! The engine, for once, was actually able to breath.

I've since rebuilt my exhaust. I went back with the same design, but I've gone to a much larger diameter pipe. I've not flown it since doing this, but I'm quite positive the result will be positive.

No matter which exhaust you use, if you want performance, and you're not worried about noise, go with large-volume system. An engine has to be able to breath in order to run at peak performance. If noise is an issue, the B&B style muffler is about as good as you're going to get.

Hope this helps.