Keep one thing in mind too... a "Turbo muffler" has nothing to do with forced induction, it's a marketing term for an unpacked muffler (flowmaster knockoff) basically.
It's gonna sound like crap on a 4cyl, you'll really dislike the sound.
it seems like a few of you are thinking "turbo" muffler like dynomax i think the original poster is talking about a Turbo based system like the flyin miata turbo or enthuza M1 turbo racer http://www.enthuzacar.com/m1turbo.asp
still a straight through but larger piping, and a lot louder,
so nappy, the turbo system will sound similar to its N/A counterpart but siginificantly louder, the reason is the turbo system is counting on the actuall turbo muffling alot of the sound. it wont sound bad but unless you like really loud noises i suggest you at least get a resonated midpipe. and keep your cat
like me im runing 2.5" "cat"(or lack of) back to a borla boomer muffler, good for turbo, but loud as hell, i go to wot at 5k+ rpm and it really announces that its there,
but if you want my honest opinion, and coming from experiance, most crush bent custom exhaust sound like ass, im not sayin all but most. between the turbulance from the crush bend and the "tinnyness" of the aluminized steel tubing you get alot of buzz mixed in,
stainless piping is alot more resistant to that echoing tinny sound, and the mandral bends will make you a hell of alot happier when you finally get that turbo, (and at least a good 2-3 extra hp) and by the time you spend about $255 for an HKS hipower universal muffler, whatever for piping and $50 for labor to put it on(what my shop charged me), its not really that much of a price differance to the enthuza, borla, etc usually going for 330-350 where you are getting mandral bends, stanless piping and actual research and development to make garunteed horsepower
actaully right now im trying to get rid of my system for about half that but am also spending the extra to import something JDM