The cat-back system replaces everything from the catalytic converters back, hence the name cat-back system, it consists of flowtubes (from the H pipe to the mufflers), the mufflers, and the rest of the pipe out and new tail pipes. An H or X pipe is where the cats are, the offroad versions have no cats, and are not emmisions legal. Some H and X pipes have only 2 cats and are 50 state legal.
Running just a cat-back system with the stock H pipe will be quieter than a system with both an aftermarket H or X pipe and a cat-back exhaust. A cat-back system by its self should provide anywhere from 5-15 HP depending on the other mods you have on your Stang.
90 LX, Previous 4 cyl.
408W In the Works
TW FAC's, Jay Allen cam, Super Victor 2001 V6 5 Speed Daily Driver
Windstar Intake, Dual Exhuast, CAI, Headers
Best ET: [email protected] mph (on 18's)