Long tubes eliminate where the factory places the cats. If you go with long tubes and need cats they will be in the h-pipe beneath the floorboard farther down the line from the collectors. They appear to be placed where the 99-04 Mustangs had the rear most set of cats (99-04 has 4 cats, 2 on each side).

 

So your saying, if I ordered Long Tube Headers and high Flow Catted X-Pipes, something will go wrong? Or I will have fitment problems?

Im really sorry, dont flame me please..im a noob when it comes to header/xpipe areas....

 

If you buy the whole kit from them it will bolt on. There are several kits out there for the 05. Most offer cats or no cats choice.

 

Long tubes with a catted H-pipe(or X) will fit just fine. Your catalytic converters will be under the floorboards instead of angling up along the transmission tunnel toward the engine compartment.

A side benefit, is that the heat you feel on your feet from the stock catalytic converters will be gone. The comp cats are a bit cooler, and moving them under the floorpan puts them away from your feet.