Long tube headers. How can they be generic?
 

One of the common upgrades in the Mustang world is to install long tube headers. Lets avoid a deep discussion of how long tube headers improve performance, lets leave it with 'they improve exhaust scavenging'.

The thing is, how can one make a generic long tube header? To really get the scavenging effect, doesn't the length and diameter of the tubes need to be tuned to the cams? Doesn't timing come into play here?

I'm sure adding long tubes will get you a few more hp regardless of your cam setup simply because they flow better.

Discuss....

Tuning headers for individual cam timing sounds like cha$ing perfection--like F1 level stuff.

I have always heard on a header collector for a race car, they run the engine wide open on a dyno (or otherwise) until the header collecter (just downstream of the end of the header) starts turning red from the heat. They then cut off the pipe an inch or two beyond the red area.

As far as determining the equal lengths of each header tube, it does depend on how many obsticles suchas motor mounts, starters, and steering controls come into play that need to be routed around. I'm sure there is a formula out there somewhere that outlines the most advantageous diameter with which head/valves size you are using, and what the best length of each diameter should be used.

Sorry, i'm not an expert, but know just enough to keep the converstation going.

I think the manufacturers of headers are building a unit that will fit MOST applictaions. If you are truly building a deep breathing monster, then specially built hearrds are a must.

I spent countless hours over two days with a 3.2 911 race car on the dyno swapping different headers and collectors while Steve Wong (911Chips) worked at fine tuning on his laptop. We compared 1.75", 1.63", and two and three-stepped stainless steel tube diameters, all open (without mufflers) to keep apples to apples. All had their strengths and weaknesses somewhere in the RPM range, but non produced more than 2% in additional HP anywhere in the range.

I think a good off-the-shelf long-tube vs. a custom tuned long-tube would not be more then a couple HP difference...and the 4 or 5 additional HP would come at a huge cost.

EDIT...SW could make a better improvement with a few taps on his laptop keyboard to optimize A/F and timing than any header could produce on it's own.

Having the utmost in scavenging won't make a measurable difference if you're running a muffler.

Need reverse cone megs and those are ear bleeding awful on the street.

Cost vs. Benefit....in the Mustang world, It seems the aftermarket brands each have their own following. I did read complaints on the Bullitt board about Kooks and fitment issues. But that SN197, not SN95 like your car.

A crossover pipe aft of the collectors is the key to good performance from generic tube headers.

A set of SSIs hooked up to one of those mufflers with the two pipes at both ends that cross inside of the muffler like an X will get you great scavenging, but they are loud as heck.

I think after about 250 HP you start to lose top end because of the header pipe diameter, but how many of our cars exceed that ?

In my drag racing days, our "poor man's" approach was to paint a stripe down the collector and cut it off a couple of inches past where it quit burning. Everyone knew this "top secret" tuning tip...

Speaking in generalities, longer tubes are for low end power, shorter tubes for high end. There is a lot of leeway in each range and overlap between the two.

Unfortunately, V8's introduce a whole 'nother conundrum - they are not even fire on each individual side. That's why we see the "snake pit" on top of old Ford GT40's and many F1 cars of the day; they were trying to divide the motor into two even fire fours. Our flat sixes do this naturally, so there is no need to even try to make some elaborate cross over primary system like that.

Anyway, the fact that V8's are not even fire on either individual header plays hell with exhaust tuning. As such, each primary should theoretically be a different length, depending on how long it's been since another hole fired on that side and how long it will be before the next. It's kinda a no-win situation.

Then there is fitment on the car. That will dictate a range of primary lengths that can be made to work. Honestly, without a handle on the even fire problem, this is the thing that matters most - do they physically fit in the car, past all the other crap?

That kind of it in a nutshell. If you are in fact building something unusual, outside the range or normal bolt-on goodies, you likely have more physical room in which to play and then start working about primary lengths and such. In the end, for the vast majority of applications, it just has to fit the car.

They are generic because length will scavange best on the lower end of rpm, flow, and timing while the od is large enough not to restrict the flow at higher rpms for the widest cam and timing options assuming it is a 5 liter motor.

I also expect even advertised as equal length tubes will vary by a few inches per cylinder. That might not be all bad as it would average the torque and hp over a wider rpm range by boosting some cylinders at lower rpm and some at higher rpms

All I can say is:

Cheap headers will piss you off to no end. Don't buy cheap headers.

Buy cheap headers and you will learn to use tools in ways never thought of- just to get them to seal or fit.

rjp