Depends on what you're looking for. There are many different varieties of a "Dual Exhaust System"
The stock configuration on the v6 mustang is headers, 4 cats, y-pipe, single exhaust piping, muffler, and tip.
The cheapest way to get a dual exhaust, is the
True Dual Exhaust System setup. What this means is that the exhaust configuration is as follows: Headers, 4 cats, straight piping, muffler, and tip. There is no crossover involved (y-pipe on the stock config.). What's done in a True Dual exhaust setup is cut the y-piping in half so the pipes do not cross over any longer, remove the muffler on the left side exhaust. Put new muffler on left side piping. Fabricate new piping for right side exhaust. Install new piping. After install of piping, muffler installation occurs. After this, the over axle piping is fabricated and muffler tips are welded on to the piping completing the procedure. "True Duals" as they are called are the cheapest and most effective way to get a dual exhaust on a v6. They also increase the sound the most
The next way to do the dual exhaust is to have a crossover pipe. The y-pipe, x-pipe, or h-pipe. Y-pipe is the stock configuration and really can't be converted to a dual exhaust unless its cut in half. The X and H pipe are exactly like they sound, no pun intended. While on the topic of sound, h-pipes will give you a more mellow sound compared to the x-pipe which is between the sound of the h and running true duals. Depending on local laws, if you decide to go with the crossover setup, you must check to make sure if you need all 4 cats on. There are two types of crossover pipes. Off-road and Catted. Off-road pipes don't have cats and are not exactly worth it on a mild to stock v6. The loss in backpressure from not having cats will hurt your low-end power. Catted pipes are more expensive but they have cats so your car will lose minimal to no power and could possibly gain a few. Just make sure to follow local laws, wouldn't want a fellow stanger to be pulled over!
The diameter of the piping is the next important subject. If you get a true dual exhaust setup, I recommend the stock diameter size, just for the matter of it being cheaper to get one pipe made rather than both sides. If you plan on and are almost 100% that you're getting a supercharger though, you must go bigger. For the crossover setup, stock size piping is good as well, but you can go a little bigger if wanting to.
Here's the sizes that are best for their applications:
1.) Power Adder: 2.5" Piping
2.) True Dual: 2" Piping
3.) Crossover: 2"-2.25" Piping
Next and final subject is mufflers. Mufflers are very subjective to say the least. There isn't a specific muffler that's going to get you more power than the other, they are more based upon sound. There's plenty of opinions about exhaust out there, you just got to find one that suits you. I'll try to sell you on my exhaust of course but that's because I'd like to see more people run it because it sounds so good (to me).
I have a true dual exhaust with Pypes Violator Mufflers. I love the sound, the clip that I'm attaching is when my car was basically bone stock.
Garages > Schumi23's 1998 Ford Mustang - FQuick.com
I bought my mufflers off of Brenspeed's ebay account for $50, I believe they're selling for $110 now though.
If you're looking for some other opinions go to youtube and type in v6 mustang exhaust (or certain brand of muffler name) and see how it sounds. Here's a thread over at another site I frequent that has some exhaust notes in it.
Exhaust Opinions - 3.8 Mustang Message Board
All said and done, you should not be paying more than $500 total for an exhaust system, if you are you're getting ripped off. Which brings me to my next point, if a shop doesn't know what True Duals are or say that it's not legal, DO NOT UNDER ANY CIRCUMSTANCES go to that shop, they have no idea what they're talking about.
I do believe this thread should be stickied that way I don't have to keep repeating myself. *HINT HINT*
If you have any more questions, please ask.
