I was wondering how much horsepower i should expect to gain by putting in performance exhaust headers into my 5.4 liter. Ive heard claims that I could get 1-3 or as much as 20. Ive also heard about getting 1-2 extra miles per gallon. Responses from people who have experimented with them would be much appreciated:

 

Might want to specif if you are going the route of something like the JBA headers, or the Kooks long tube headers. to get something more specific to what you are looking at.
Neal went from the JBA and Flow Master combo to LT headers and the MagnaFlow system and cut a bit of time off his 1/4 ET.

 

330cid
there are alot of mods i would do before headers. i think that for the cost, the installation, and the performace gain they are not the best up-grade.
electric fans, pulleys, air intake, chip, magnaflow cat back exhaust to name some.

as for Neals gains, i know he likes them but i have never seen any before and after 1/4 mile times or dyno numbers.

if you were to get them, sscully is correct, the long tubes are the way to go. just remeber that to get the full benefit would require an upgraded exhaust after the header so it would be nothing to drop over $1000 on an exhaust system.

 

Couple years ago I read an article in Sport Truck where they tested mods to a 98 5.4. They first installed a K&N FIPK and saw a minor increase on the dyno. Then they put a Gibson cat-back on and got minor gains. Last they put on Gibson headers and saw 0 gains in hp or tq. They said it was louder but thought the head design was limiting the benefits of the headers. They felt that the 99-present engines MIGHT see a gain with headers due to the better head design.

 

I had headers on my 2000 5.4. They do very little IMO. The NA 5.4 uses the same exhaust manifold as the Lightning SC 5.4. The Lightning guys claim no header short of long tubes do squat and they do have time slips. So, the regular 5.4 exhaust manifold is just fine for 380+ horsepower. They do have a unique sound and give you all of the problems associated with headers. BROTHERDAVE hit the nail on the head, headers are way down on the list.

 

I agree headers probably do not do much in the power department, but if you are replacing broken manifold studs and fighting exhaust leakes, they sure work well. At any rate if you are going throught the trouble of taking of the exhaust manifold to replace the gasket, you might as well stick headers on. If you use the stainless locking bolts and felpro gaskets you only have to do it once. I believe all the data out there about HP gains with headers, but if you ever get a chance to examine some stock exhaust manifolds, be prepared to be underwhelmed with the design. I have seen six cylinders with more breathing potential.