Before I ask my header question, I thouhgt of another one. In a muffler, would getting a smaller inlet/outlet(2.5") result in back pressure = more torque or should I just match the size of the pipe 3"? Now for the headers question, what do I look for when buying headers? What distinguishes one from another?
thanks
oO

 

Headers will kill your low end. If you spend most of your driving drag racing then disregard..Exhaust is one of the area's where you are not gonna pick up much power but you can change the way it sounds and some people like that. Most of the time going with more flow hurts the low rpm torque curve. Engines are designed with back pressure to increase velocity at low rpm. Also as soon as you open the exhaust system on most vehicles your mileage goes down cause it needs more fuel at low rpm's to stay in closed loop.....

 

From what I have read here, headers don't kill the low end torque on the V10. There seems to be enough back pressure through the cat to retain the torque.

 

Ok, no more back pressure talk. Back pressure kills performance - period.
Factory heads are designed for the best power/economy over the normal RPM band( Not the RPM band I like use in my V10).

For factory heads think of this picture(only an example) a large opening(1), followed by a smaller opening(2), then a larger opening(3).
As the exhaust gasses leave from exhaust port(1) they enter the smaller opening(2 - factory heads), this causes the gasses to speed up going into(3). What this does is create a scavenging effect IE. the gasses leaving at (2) are moving faster than at (1) there by pulling the gasses from (1) out. At some point however the amount of gasses in(1) can no longer be pulled by(2) as the opening is not large enough and you start to lose power (At higher RPM).
Headers remove the action of(2) the pulling of the exhaust gasses away, IE, not as much power at lower RPM, but more power at higher RPM because the restriction of(2) is removed. Power is not lost, it is higher peak, but moved up RPM band.
Many headers try and remedy this effect by adding a scavenger tube where they(exaust tubes) come together. IE exhaust from tube 1 pulls gasses from tube 2.....

Here is a link for some further discussion. I have no interest in this co, do not represent them, nor recommend them. That is your own decision.
They do have a nice explanation of header basics.
http://www.ssheaders.com/header.htm

My 2 cents..BWDIK

 

and here i thought this topic was already beat to death.... anyhow, i do this stuff for a living (although not on a V10 ford), but the physics are still the same. the trick to getting more out of any engine, is getting the combination right. a well made set of small tube headers, along with a free flowing y pipe (or an H or X pipe in a true dual system) will open the door to more torque AND horsepower. even more can be gained with a free flowing cat back system as well. that being said, a set of headers that are too big, too many bends, crushed pipes, etc. are not going to help at all, and in fact will hurt performance everywhere.

just my 2 cents...

 

thanks for the help everybody

hey pancartom,
do you have any suggestions for " small tube headers " for my
02 f250 5.4 v8?
thanks
oO