Header explanation? Please

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Small Block

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Let's talk headers. First off, whats the goal when someone thinks they want to put headers on a car? Most times i'd say they want more horse power but in some cases they're looking for milage. They all come with different diameter tube sizes. Whats the pros and cons with that. How about tube length? Should they be equal? What's ideal? I hear people talk of "Tuned" headers. Are all headers tuned? If not, what's the difference in tuned and regular. I'm asking because i dont know. Time for you gurus to chime in here and let's get this explained so a hillbilly can understand it.
Small Block
 
Header diameter and length depend on the motor you have as to horsepower and torque. The smaller dia and longer length will yield more lower end power (torque) but again depending on the motor. A high revving motor with more cam and compression will want a larger dia header and a some what shorter length. As far as tuned all the tubes will be of equal length. I hope I am correct Bill. Maybe perfweld will chime in as he builds headers for a living.
 
I think that equal length is tuned,the concept being when the power stroke from one cyl gets to the collecter it creates a vaccum and helps the next power stroke to come through in a rythem. But I could be way off?
 
And speaking of perfweld I really want a set of good stainless shorty's for manuel steer,4-speed, 67 cuda.
 
Equal length - better scavinging of the exhaust, per cylinder. The other cylinder that just fired, and is moving exhaust out, pulls the next firing cylinder exhaust out with it. And less restriction than an iron manifold, that was made just to clear everything.
36" is a start. Put 18" extensions on the header, sprayed with rattle can paint. Make a full run and kill engine. The point that the paint stopped blistering off is the optimum length the current engine wants. cut the pipe there.
! 7/8" = more torque. More = single plane, all rpm to use, like a 350 chebby. Mopars win with the torque with the longer stroke, and close to squared bore/stroke. Torque usually wins.
Unless all-out pro stocker, 1 7/8", tune the extension.
 
Bill, all I can say ( being of the hillbilly mindset myself ) is I know they work for power. I had a 77 Blazer w/ 30? 2 bbl/4spd granny 1st gear/ 3.?? ( highway ) rear end and had to downshift up steep hills. Had headers installed and zoom zoom up the hills. I would have them on the 65 Dart if they wern't so expensive for the pre 67 A-bodies.
 
also another rule is that the primary should be the same size as the exhaust valve diameter. so a 1.90 exhaust valve would be a 2" primary tube.
 
A REAL tuned header is one that has the same reversion characteristics in each primary tube. Same exhaust volume, same backpressure and so on. not necessarily all the same length tubes, but they can be. Few companies actually make real tuned headers anymore. Usually, what has been adopted to mean a tuned header is one with equal length tubes, but it's not really the truth. As you can imagine, real tuned headers are very costly and only custom made. I think for a Mopar, there is only one answer. Which one fits best. Everything else that you may get with the one that fits good, is just icing on the cake. I think all headers will flow much better than any manifolds, so there's your performance difference right there. Few applications IMO actually NEED a real fully tuned header.
 
StrokerScamp said:
A REAL tuned header is one that has the same reversion characteristics in each primary tube. Same exhaust volume, same backpressure and so on. not necessarily all the same length tubes, but they can be. Few companies actually make real tuned headers anymore. Usually, what has been adopted to mean a tuned header is one with equal length tubes, but it's not really the truth. As you can imagine, real tuned headers are very costly and only custom made. I think for a Mopar, there is only one answer. Which one fits best. Everything else that you may get with the one that fits good, is just icing on the cake. I think all headers will flow much better than any manifolds, so there's your performance difference right there. Few applications IMO actually NEED a real fully tuned header.
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Cool, somebody is old school, and can explain reversion. Great, go ahead, as I forgot it in my old age, lol.
 
Robert Yates Racing did a test of primary length being equal and unequal and saw no discernable difference in performance as long as the shortest tube was the proper minimum length.
 
There was a segment on one of the car shows I watch that explained it well. I will try and look it up.

Basically, the main function of the different tube lengths was to compensate the length of time the outflow is in the pipe to keep the back pressure from fighting the outtake of the other cylinders.
 
Ok I found the episode of "Two Guys Garage" that had the exhaust flow breakdown:
[ame="http://www.youtube.com/watch?v=n8VlynaUVO8"]http://www.youtube.com/watch?v=n8VlynaUVO8[/ame]

At 2:13 he goes into explanation. @ 7:07 he talks about the "pulses" that make the tubes longer or shorter.
 
green1 said:
Cool, somebody is old school, and can explain reversion. Great, go ahead, as I forgot it in my old age, lol.
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I'll see what I can do. In the late eighties....I think 87, not sure, I attended the last manufacturer's show at Speed distributors in Atlanta. Speed Distributors was a wholesale only automotive outlet similar to Summit, but much smaller, that sold to retail speed shops across the southeast. They are now defunkt. they used to host a really cool show anually, where they would have all the big wigs from all the major brands there. Anyway, the last time I was there, I actually got to talk to Doug Thorley hisself! We had a nice chat and that included his thoughts on exhaust reversion. In a nutshell, I remember him saying that all reversion is, is the exhaust trying to move backwards in the header tubes on overlap (when both valves are open) at low engine speeds. He was a very to the point and astute gentleman.....even genius, perhaps. I really used to enjoy those shows a lot. Got to meet several legends. Dick Landy, Doug Thorley, Don Garlits, Don Prudhome, Vic Edelbrock, Smokey Yunick...and even more. We were just a small machine shop in Macon, but we ordered enough speed equipment from them each year to always get invitations, so we always went. I miss those days.
 
Informative thread!! What about "stepped" primaries? Do they increase torque? How big is the change in diameter? Is this only good for smaller engines (if at all)?
 
also to make full use of a real tuned header you want an equaly tuned intake side of your engine.
the thought behind a stepped header would probably be to be able to use the velocity of a smaller primarytube when still havig the greater flow of a bigger tube and the steps could probably stop reversion also but i feel most comercialy available headers use the smaller part of the stepheaders for easier acces to headerbolts in aplications where the boltspacing is to tight to uese a bigger tube.
not an expert just thinking alitle free
 
duster340 said:
also to make full use of a real tuned header you want an equaly tuned intake side of your engine.
the thought behind a stepped header would probably be to be able to use the velocity of a smaller primarytube when still havig the greater flow of a bigger tube and the steps could probably stop reversion also but i feel most comercialy available headers use the smaller part of the stepheaders for easier acces to headerbolts in aplications where the boltspacing is to tight to uese a bigger tube.
not an expert just thinking alitle free
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RIGHT! Your comment goes back to the "match it all up" theory. If the individual parts of the package aren't matched, you can forget getting the absolute most out of a combination.

...and on the stepped header thing.....IMO, the stepped headers are good for two instances. In tight engine compartments (B/RB in an A body) or with mild to moderate combinations. The smaller first primary setion allows for some velocity increase going into the larger primary section.... kinda like a venturi effect with a carburetor. The stepped headers usually aren't much of an advantage for really powerful combinations.....say 500HP and up. But in the A body, we don't have much of a choice. That's why the TTI and Schumacher have HP limits clearly marked on their web sites.
 
I really appriciate the intelligent comments here as i knew we did have people on here that have brains. Good stuff Maynard. Let's see if i retained any info that was submitted. If i heard it right, one needs SOME back pressure. If that's correct then if your exhaust valve i a 1.80" on the 440, then it would be ok to have a tube of a minimum of 1.75" thus creating a back pressure or venturi. The ill efects of unequal length tubes can also be corrected by useing cross overs or an H pipe. Am i on the right track. Tell ya what we've got. We're doing a 64 Savoy 2 dr post car. We want to do it right. The motor is a 440 punched out 30 over. It has 2.18 intake valves and 1.80 exhaust valves. Compression is at 12.5. Harlan Sharp rollers on top. As of now it has an Edelbrock DQ air gap intake on it with two comp series 500's. It's a 68 dated 440 and was sold to me as a 6 pk motor. I took it to the shop and had em tear it down and start over. It had new, never ran standard trw's but felt they were a little sloppy so we put in a set of 30 over trw's in their place. We're gona stuff it in and see where we're at. Just with what you know, what header would you start with if you were going to run it down the 1/4 or the 1/8 th. I have the choice of a 3.91 rear or a 4.68 rear gear all attached to an Eaton TruTrac gear drive sure grip. Any ideas guys?
Small Block
 
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