The Cats: MagnaFlow Tru-X Pipe with Cats
    We orignally planed on leaving the stock cats in place and adding an x-pipe down the road, since there are stories of many 2003 Cobras that run into the 11's with the stock cat pipe. However, MagnaFlow convinced us that their Tru-X cat pipe was a step in the right direction, and after taking a hard look at the pipes in person, we didn't need much convincing. We selected the MagnaFlow 2003 Tru-X crossover pipe with converters (PN 93335, retail price $687.60), which is a 2.5" X-pipe that fits both the 4.6L GT and the Cobra from 1999 to 2003. This is designated "Off Road Use Only" because it is illegal to replace cats before 50,000 miles for non-mechanical failure reasons. As such, these cats are not CARB-approved in our specidic application. However, the reality is, according to most Mustang tuner shops, they will pass a smog check in 99 percent of applications, so make your own judgements.
    In fact, according to MagnaFlow, their Mustang catalytic converter is designed to do two jobs: reduce emissions and improve flow. "The emission reducing task is taken care of by two high-efficiency ceramic catalysts that use heat and a precious metal coating to burn off harmful elements. Flow improvements are accomplished by utilizing fast-flowing mandrel-bent tubing and incorporating MagnaFlow's Tru-X crossover pipe that replaces the inefficient factory H-pipe."
    In a stock 2003 Cobra, the cat pipe is an H-pipe design. The MagnaFlow X-pipe is a NASCAR-inspired design that improves high-rpm horsepower and torque due to the convergence of exhaust pulses. The 2003 Cobra tuners told us that many aftermarket X-pipes with higher flowing cats will drop some torque down low, but pick up horsepower and torque over 3,000 rpm. Since we didn't do an apples-to-apples dyno comparison, were we unable to verify this. However, dropping a little torque down low is a good trade off since the car is traction limited as it is. Installation of the X-pipe was a breeze. Home installers note: dislodging the stock H-pipe took the use of plenty of WD-40 on the header-to-cat-pipe bolts!