For the peole wanting headers but not having 700 for kooks headers or taking a chance on jba headers here is a cheap and almost free performance improvement. I ported a set of production 4.6 cast iron manifolds. It should help make more power from improved airflow. I have not done any seintific testing to prove this but it should be true. On the factory 4.6 manifolds they have about a 1/8 inch lip inside the manifold reducing flow. I cut this out and enlarged the outlet opening to improve airflow. The driverside is difficult to improve flow because where the factory indented it so that it was easier to install the manifolds from the factory. I had to cut more out of one side than the other. If you look close at the inside of the driverside you can see a little bit of the ring still in there. It is much shorter than before.