I've been running JBA shorty headers, stock mid-pipes and Flowmaster mufflers on my 2005 GT since it was new. While it sounds great and I "feel" increased hp, am I remiss in not installing X type crossover pipes? All comments please.

 

There is certainly horsepower to be gained by upgrading to an offroad x-pipe. It's a difference you can feel, for sure. This is the pipe I used on my '06 GT and it made a noticeable improvement in power and sound.

http://www.uprproducts.com/mustang-o...x-pipe-05.html