OK, now that I went with a Magnaflow muffler I believe it's time to look into the air intake and headers. The air intake I'm still planning on modifying the stock, so that will be awhile due to time contraints. But what about headers? I did a search on it on this 04/05 forum and there wasn't a lot of information available. I did see that some headers come that you do not have to replace the stock pipes and that would be the way I'd go. So here are the questions:

Have you installed headers on the 04/05 F150?
Have you installed headers on any previous truck and what was the result?
Which brand(s) are the best hp?
Which brand(s) have lowest failures and low maintanence needed?
If new headers are installed, what type of hp increase could you see?

That's all I can think of for now, but any leads will be appreciated.

 

This is all from what I have read and heard..... Putting headers on a stock, naturally aspirated engine wont make much difference in performance. I spoke with my local mechanic about headers. He said mostly, you will notice a difference in sound. he also said steer away from "shorty" headers. He said to really free it up at the exhaust ports, you need long. flowing headers. the shorty headers, especially the ones that have the tight, winding, tubes, dont really make any difference in power. But you will notice a little power from the longer, flowing ones.
His credibility is just from hearing testamonials from people that have them installed.

Not if you were to Turbocharge it, of Supercharge it... headers will make a noticable difference in power, throughout the RPM band.

This is my opinion (worth nothing).. I would'nt put on headers unless it was supercharged, or unless you put on 4-valve heads. I personally dont believe the engine "needs" to be free'd up that much. I dont believe it will help. But if you do want headers, I would recommend putting on a high-flow intake at least... I know you already have the magnaflow exhaust.
This is all just what I have heard..... There are a couple of guys in other forums that have put headers on they're '04... said it made a little difference in power.
EDIT: And the high quality, ceramic coated ones are expensive too. You want one that hold they heat well and dont disperse it into the engine bay.