Q:
A: an axelback replaces the muffler, keeping the stock midpipe, s pipe, etc and catalytic converter. they are generally more quiet and since the exhaust piping is stock, there will not be much increase in hp. however, the catback systems replace the whole exhaust system, removing the secondary catalytic converter. they produce much more horsepower than an axleback would because the catalytic converter is restrictive and lowers hp, so removing that would allow for a greater flow of exhaust fumes from the engine. here's an analogy: in a cup of water, try blowing bubbles through a small, coffee-stirrer straw. its pretty difficult, but then try blowing bubbles throw a normal sized drink straw...it's a lot easier. see what i mean? the catback system is like the bigger straw which lets the air flow more freely and therefore puts out more power. there are many catback/axleback exhaust systems out there, some brands i know of are: 1) tanabe 2) greddy 3) megan 4) tsudo 5) hks i know there are much more other ones out there, go to a scion xb forum and ask around. people there will help you out much more than we can here.