I was just wondering, but what kinda hp gains would I get say from a cat-back system compared to just a performance muffler, and what causes some cars to sound like tin cans and some have a deep throaty sound ?

Don't mean to be a Search-Nazi, but did you do a search before you post??

Anyhow, I think this link will answer most of your questions concerning exhaust, from whose who down to how to install them.

http://www.se-r.net/header_exhaust/index.html


Hope it helps.

Difference in shape of the muffler as well as internal design and (what I call) stuffing dramatically alter the sound of the exhaust as well as the size of the pipe and how open it is from the exhaust ports to the tip. Aftermarket header and cat will make it sound more gruff whereas the stock header will make it sound more..well, muffled sort of. Straight through mufflers, N1 styles or the round ones are generally lighter and designed more for reducing backpressure rather than sound, the oval shaped mufflers tend to give it more of a muscle car sound, deep and throaty but that sound can be different between models of the same shape depending on if they put fiberglass inside the muffler which generally darkens and muffles the tone of the exhaust. You'll gain more hp from a catback since you're replacing all pipes and the cat all the way back to the muffler, replacing only the muffler won't make a huge difference but of course, replacing the header, cat and muffler will net you the largest hp/tq gains. I hope that better answers what you're asking.