Starting in 1986, the Mustang (for the first time, I may add) came equipped with a true dual exhaust system. The factory system comprised of shorty headers (exhaust manifolds) each side flowing through a catalytic converter, on through an H-pipe and out the back via high capacity mufflers. Manifold back, the tubing is all stainless steel and approximately 2.25" in diameter. The major restriction point in the stock system is the exhaust headers. Swapping these out with a new set of aftermarket headers will yeild power gains and a richer tone. Furthermore, they lay a solid foundation to support a high horsepower engine.
Swapping the stock shorty headers with an aftermarket design in your Mustang is a very smart choice. The stock Fox Body headers are a major restriction point in the exhaust system because of their inconsistent shape. The Ford fitted headers are of a cast iron variety and were not made exclusively for the Mustang. Due to mass production for different vehicles, very sharp kinks and bends in the stock headers had to be made and severely reduce airflow. At some points, the tubing may be squeezed to only 1” cross-section! Amazingly, however, the stock heads are good for a 5-7 HP gain over the 1986 header design… who would’ve thought? Regardless, they are a major choke point on the exhaust system.
Headers from the likes of BBK, Ford Racing, Pypes, JBA and other aftermarket exhaust companies all have all designed mandrel-bent Foxbody 5.0L specific pieces to eliminate these factory-header problems, maximize airflow and still be a direct bolt-on without clearance issues. Their offerings come in different tube diameters as well as finish, which have different benefits. Let’s go through them, starting with shorty headers versus long-tube headers.