HEADER DESIGN COMMENTS - FAQs (Frequently Asked Questions).

Under Construction GIF



What went wrong? This is an amazingly frequent question - often asked by those who chose to ignore the importance of having a well designed header and, after the installation, are now trying to deal with noticeable problems or simply the lack of performance improvement. The answer to this question as well as many other performance related questions is often more questions: "Why did you buy such a large header?"; "Why did you buy such an inaccurate (unequal length) header."; "Why did you buy such a short header?". 

What is "mandrel bending"? This is a method by which tooling is positioned INSIDE the tubing during the bending process to support the tubing so that it doesn't go out of round, wrinkle, or reduce in diameter. Because headers tend to be built in tight spaces and thus require tight/small radius bends, the inserted tooling required for these tight radii bends basically resembles a series of tightly connected balls (actually look more like discs) that "ride" inside the tubing during the bending process. Depending on radii, material, etc., the number of balls (discs) can vary from one to five. The only draw back to mandrel bending is that it is a "stretching" process so that the outer wall of the bend gets thinner. The tighter the radius on a given tube size, the thinner the wall will be on the outside. We try to warn header builders to only use the tightest bends where necessary to clear something. Mandrel bending does NOT absolutely stop the tubing from reducing in diameter, it just reduces the amount of reduction due to the internal support. In most cases, the tubing size reduction is minimal (can't be seen) BUT we have seen "mandrel" bending where the internal tooling used was the wrong size and/or totally worn out and have measured diameter reductions as much as .200"!!! As in so many other areas, there can be GOOD as well as BAD mandrel bending. (The basic process is good, but how it is implemented can vary considerably.) 




There are probably hundreds of questions (and answers) for this area. We'll get to some of them as time permits. (Send us some!?)





As you might guess, we get considerable e-mail here concerning headers and header design. We've decided to put some of those messages here for others to read. Some are selected because of their unsolicited comments, others due to our lengthy response that deals with an area of concern voiced by many yet not covered elsewhere in the website.

A response to an e-mail question concerning certain discussion in our HEADER DESIGN InfoPak:


Sorry to disappoint you but I think you've put the cart before the horse.


The most important part of a header's design is to get the tube diameter selected correctly - whether the engine is used in a daily driver situation or used for all out racing - because that diameter establishes the gas velocity inside of the header which then establishes the primary scavenging characteristic of the header. If the header tube diameter is selected correctly, the engine then produces a noticeable increase of power over a wide rpm band which makes correct size selection almost more beneficial (almost more important) for a street car than it is for a a race car. If the header tube diameter is too big, the top end power might go up a a little but the bottom end and mid-range power will actually be reduced by a far larger amount. (We've seen engines experience a 5-10% loss in power in the mid-range to get less than a 1% gain on top end just by oversizing a header by ONE tube size!) To a racer, where, hopefully, the mid-range isn't important, the 1% gain might be very important but, to the guy driving on the street, the 5% (or more) loss in mid-range power is far more noticeable than the 1% gain at high rpms (note that this assumes that the exhaust system - after the headers - is NOT the major restrictor at high rpms). Keep in mind that the guy on the street is also NOT driving at full throttle at high rpms all the time so he may actually not even notice the minimal loss of power at high rpms with a smaller tube diameter because the engine is hardly ever used that way - BUT he will definitely notice the loss in mid-range and bottom end power with a larger tube. (Note that having all of the header tubes the same length as well as long enough to function optimally in the engine's rpm range is a critical part of this design "equation" because the header has to scavenge ALL of the cylinders to the same degree if the power gain for each cylinder is to be achieved equally as well as optimally - which cannot be achieved in an UNequal length design. Another point to be made is that deliberately downsizing a header to further increase bottom end and mid-range power with an acknowledged acceptance of some top end power loss is a good "trade" for many as the loss of top end power isn't as important as is maximizing performance in the lower part of the rpm range.)


The collector diameter isn't a major concern on a street vehicle because the secondary gas velocity after the header tubes is established more by the entire exhaust system then by the collector diameter. However, when the headers are open to atmosphere, the diameter of the collector becomes VERY important because that diameter then establishes the gas velocity immediately after the header tubes. Here, again, usage determines header design. 


One thing that is VERY important in a header's design - on the street as well as on the track - is the shaping of the transition from the individual tubes to the collector outlet as the shaping of the tubes INTERNALLY, as we recommend, into a cross (+) pattern as well as the shaping of the collector itself (should have very deep creases on the outside so that the outer shape of the collector matches very close to the outer shape of the tubes entering it so that exhaust gas expansion and any turbulence induced by the outer shape is truly minimized). The reforming of the tubes in the center is also critical to reducing/eliminating gas expansion and turbulence. The elimination of expansion and turbulence of the exhaust gases as they move from the header tubes down to the collector outlet is very important as it basically determines how efficient the gases flow in that area. Done correctly, we've seen 1-3% gains in power over most of an engine's entire rpm range which means that having an efficient collector design might be considered even more important for a street vehicle than for a race vehicle because of the street vehicle's broader rpm band usage. One last element in a collector's correct design is that its tapered area (not its overall length but its tapered length) be at least 5" long - this dimension - easily measured - eliminates many of the headers on the market - particularly block hugger type headers as well as "shorty" headers where the collector tapers are often half as long (some even much shorter than that!!) as what we've seen is desirable. The shorter taper - just by itself - adds restriction to flow and, therefore, reduces a header's ability to improve performance. I should also point out that when one forms the tubes internally into a cross (+) pattern, that forming - when done properly - actually extends up into the header tubes quite a distance. In our headers we've measured this internally formed distance to be up to 2" in length which means that the TRUE transition tapered length in our headers can be over 7" long if one adds up the reshaping inside the header tubes as well as the length of the collector taper.


Most do not realize how important collector shaping is because it is not discussed much in magazines. I wonder if it occurs to anyone that the highest velocity of gases in an engine's intake and exhaust tracts actually exists at the end of a collector's taper? The air that goes into an engine to produce power is actually increased in volume considerably during and after the combustion process yet few seem to consider how restrictive a poor collector design can be or how desirable a collector design that flows exhaust gases efficiently can be.


When you referenced the IN/OUT RATIOS described in the chart in the HEADER DESIGN InfoPak, I think you got too involved in the math and lost sight of what was important in a header's design. One of the reasons why the chart exists is to get guys to actually THINK about the design relationship between a header's tube size AND the header's collector size. This is very important yet basically not discussed by magazines. Even those who realize how important selecting the correct header tube size can be most often do not even consider the collector size at all! Half of what is important they don't even think about! The chart helps many see, in a different way, how important this selection can be. Another thing to consider is that the chart you saw in the InfoPak along with the accompanying text fills up an entire page in the InfoPak. No magazine would ever print this chart - due to its size - which means that anybody reading magazines would never be exposed to this important design discussion.

When I suggested you take advantage of our Header Design Advice Service, that was done to help you make a wise, informed decision. Obviously it's cheaper to make an uninformed decision but if the actual performance of your car is important you should let me help you do the right thing. 


Thanks. Ed Henneman



Comments relating to quality.


I bought a set of tri-y headers and an "H" pipe from one of the Mustang vendors for my 289 equipped 67 Mustang and I don't think I want to bolt these things on. They look pretty shoddily made and the H pipe has a hole that actually "connects" the two pipes that's only about 3/4ths of an inch in diameter. ... 



Questions/comments about Turbo Header design.



Ed, I just received your "HEADER DESIGN InfoPak w/CD" I thought this was going to tell me how I could design my own headers. Mostly the information tells me I should buy my headers from you. I'm listening to your recorded talk ... more of the same.  


I have a 1984 Nissan 300ZX Turbo fuel injected V6. Nothing I've seen in the literature, on your web site or heard in you recorded message helps me design a set of headers for my turbo. Do you have a suggestion on a book I can buy that will help me learn more about designing headers for my V6 turbo?


Dear ...: 


I've never built a header for a Turbo so don't feel it is appropriate to talk about designing them. However, I've sold lots of parts to fellows building them and have learned considerably from their efforts (and mistakes). One thing I have learned is that sizing is very critical as it determines the velocity of the gases inside the header and, from that, greatly affects the turbo's operation.


On a number of occasions I've sold parts to somebody where they built a turbo header, ended up disappointed with the results, ordered more parts to build a smaller header, and were amazed at how much better the engine ran just reducing the tube size by 1/8"! However, that 1/8" reduction in tube diameter often represented an area change of 15-20% which is quite a substantial change. (Most guys don't think of cross-sectional area changes that vary with the SQUARE of the radius change - they just think of the change in diameter - so most don't really understand how BIG an 1/8" change in diameter can actually be unless expressed in percentages.)


I think that building a turbo header is VERY risky. I believe that the factories have spent considerable time developing their systems and question how an individual - with no test equipment or prior experience - is going to improve on their efforts without incurring considerable risk in the process. In other words, while the chance of making something better is there, the chance of screwing it up is there as well and, I think, even more likely to occur. I've heard many horror stories about this - some including manufactured turbo headers so even the "experts" don't hit the mark on many occasions. 


I think you've read/listened to the InfoPak with bias as I think you have missed many of the subtleties of good header design. Just because there was no direct discussion of turbo header design that doesn't mean there wasn't any information of value. Also - there is CONSIDERABLE discussion that has nothing to do with buying headers from us. I've tried to communicate the importance of good header design - not just buying stuff from us (which is what I see others doing) and think I'm almost unique in that regards.  I've read many header catalogs that give NO information or discussion of good header design whatsoever - just "buy ours". I think you really need to read and listen some more to the contents of the Header Design InfoPak. (Many have told me that there is so much information in it that they have read the material many times and have also listened to the tape or CD many times and, each time, they have learned something new!!!!) I noticed in your e-mail that "I'm listening to your recorded talk ... more of the same". Did you e-mail me before you even finished listening to the CD? 


Note that there is one sheet in the InfoPak (which contains our Header Parts Catalog) titled "Build Headers BETTER Than ANY you can buy". I've never seen any other header company provide that type of a discussion - which is the absolute truth for many. Where does that come across as saying "buy our headers"?


I know of no books that will help you design a turbo header - you're sailing in uncharted waters. If you decide to build a header be prepared to build at least two versions as this seems to be how it works out for many. One design that initially "sciences out" right and then a second one built later on that works better as it contains improvements based on the experiences gained from building the first header. It seems that the second one is always smaller than the first one. Again, bigger is not always better.  


One other thing: Be extremely careful about looking at turbo headers made by others because you don't know how much development time they've spent on their product. I've been building regular headers for over 40 years and feel that the header industry is full of guys/companies that don't know (or even care about) what they're doing. Some even make lots of money (you can sell anything in this country if you have the marketing ability to do so) but that's because the magazines keep guys quite ignorant of good design which is why I think our InfoPak can be so valuable to many. (I'm disappointed that you didn't pick up on this.) When I started building headers years ago, I continually looked at headers made by others - always hoping to learn something. However, I also ran tests to learn about design and, from those tests (and other experiences) saw considerable conflict with what others were doing and what I would see working better. After awhile I stopped looking at what others were doing because MY TESTS didn't agree with what they were doing which, I felt, showed me that they weren't even running tests! (The laws of physics in Minnesota are NOT different from the laws of physics in California so you should NOT have different design "answers".) For example, one thing I saw quite important years ago was collector sizing and from those early days have, for years, encouraged guys to experiment with collector sizing (not with just our headers but just overall) by using different diameters of collector extensions. In our InfoPak I give guys the facts (what I've witnessed) and also provide the parts to use to experiment with - yet I know of no one else that recommends experimenting with collector sizing. This is just ONE part of building better headers yet I saw the importance of this in the mid-60s - almost 40 years ago. Relative to building turbo headers, are you willing to try different collector diameters and hookups to the turbo to see which one works best? This is part of what you must do to optimize design. Did you see our recommendation on shaping the ends of the tubes (where they enter the collector) into a cross pattern to improve flow? If you didn't pick up on this as a way of building a better turbo header, you REALLY missed something quite important. 


Thanks for your comments. Ed Henneman


Questions about benefits of paying attention to header design on a "street" vehicle.



> Is there any significant benefit to header tuning design for a roots 

> supercharged street rod motor?... like an early dodge 325 hemi. in

> a 37 chevy sedan /automatic tranny 4l80e, big meats in back,& a 3.25

> ford 9" .........for hiwy. rod runs & the occasional drag?

> ????????????@netzero.net


Dear ????????????:

Having a well designed exhaust system is definitely important for a street rod - assuming that one wants the engine to perform at its best.


Good street performance entails building a motor that has a broad power curve plus one that runs well at part throttle (as most of the time, on the street, the engine does not run with the throttle wide open).


These "car usage requirements" mean that the headers cannot be any larger than absolutely necessary or even designed slightly on the small side so that bottom end and mid-range power is maximized. The header tubes must be long (at least 34") so as to also maximize bottom and mid-range power. A well shaped collector transition will improve flow at all rpms which means performance goes up even more.


Even though you have a blower, most of the time (due to the usage of the car) it will not actually be improving performance as it will not be producing any amount of boost during normal use - yet will be CONSUMING power ALL of the time. This makes it actually MORE important to pay attention to header design so that the negatives of having a blower are minimized or, at least, dealt with. 


I've looked at thousands of blown street rods over the years and it always amazes me how terrible the exhaust side of the motor is done. Looking at what has been done by others means to only repeat their mistakes. I suggest you order our Header Design InfoPak to begin to understand the REAL importance (and benefits) of having a well designed (efficient) exhaust system. Read about it on http://www.headersbyed.com/moreinfo.htm.


I hope you spend the time to go through our web site as well as read/listen to the contents of the InfoPak as you have much to gain by doing so.


Also - did you know that we have the header flanges for your engine? They're listed on the web site. 


Thanks. Ed Henneman 


P.S. The absolutely worst header to use is a block hugger style design as it is way too short, has unequal header tubes, and usually has a collector with a very short transition length that is also not shaped correctly (i.e., a collector design that is very restrictive to flow). I've talked to street rodders in this area that have switched from exhaust manifolds to a block hugger style header and not only found that performance got worse but the engine ran 20-25 degrees hotter afterwards. If this happens on carbureted engines, what's going to happen to yours that is blown? It has to be even worse! It wouldn't surprise me at all to see you lose 15% or more power in the mid-range - particularly at part throttle - if you do what is usually done. Gas mileage will also be much better if the exhaust side is optimized for efficiency. Relative to header design, this means designs very much different that what seems to be typically used in street rods as street rodders usually pick form first, function second (often decidedly second). I hope that you are different from the majority.  



Questions about coatings, header wraps, and performance gains.

Dear Jim:

I haven't seen ANY well executed tests that back up the performance gains claimed by the coating guys. I will accept that the coatings, by insulating the header and keeping more of the heat inside the tube and, therefore, NOT raising the under hood temperature as much as an uncoated header would, would give a modest power gain due to the air temperature being lower (which means the air density is higher). However, when they talk about coatings increasing the gas velocity inside the header to promote efficiency, I have to view that as a two-edged sword. Considering that one of the most common errors committed by guys is building or buying a header that is too large (which means the gas velocity inside the header is lower than it should be), coating a header would cause the gas velocity to go up - getting closer to ideal - and that might produce a minimal power gain. The other "side of this two-edged sword" discussion would be concerning the guys that already have the correct header size which means the gas velocities inside the header would be optimized - wouldn't they LOSE performance because the coatings would increase gas velocities beyond what is correct and then restriction would set in? (Also - one should NOT think that if he buys a header that he knows is too big, that coating the header will compensate for that error - the claimed gains in power don't equate to an error of one header tube size.)

The only way I could accept that coatings actually increase performance would be to see somebody run "design optimization" header tests first - tests run to select the absolutely best header design for a particular engine. This would require testing the engine with at least THREE different sets of headers - all absolutely identical (port match, collector design, equal length AND same tube and collector lengths) and then determine the correct tube size (at least three diameters would have to be tested as we must know what is too large and what is too small to know what size actually is correct). After the tube size is determined, then one would have to test for collector sizing and this would also involve at least three different collector sizes as well. (After determining the correct collector size one might want to go back to double check that the header tube size is still optimum - which means more tests.) THAT type of testing would, at least, determine the correct header SIZING for the test engine. Then we would have to run the test with two sets of headers of the optimized design - one coated and the other uncoated to see how the coatings affect power output (tests would obviously have to run the same day). (A third choice would be just to paint another "optimized" header externally with an available high heat paint to see how just painting the exterior affects power.) At the same time we are running these test, we would also have to be double checking ignition settings as well as carb adjustments to make sure they were correct (or run the test with a computer controlled engine), otherwise tuning errors might affect the results enough that the test results would have to be considered invalid. These "test procedures" would have to be run at least a dozen times on a dozen different engines so that we could actually validate that the coatings worked (or did not work) consistently so that we eliminate any "fluke" test that might occur. Who is going to do this? We're talking tens of thousands of dollars in header construction alone without talking about the thousands of dollars of dyno time. People believe the claims that the coaters make - so why would the coaters spend ANY money and run the risk of disproving their own claims? It's not going to happen!

Header wrap can destroy headers as it is a very good insulator and can push the header tubing temperature beyond what it is able to handle long term. We, as well as a few other header companies, won't warrantee a header that has been wrapped. I have had phone conversations with guys who wrapped their headers and burned them out in less than a year. Worst example I've encountered was a phone call from local guy with a motor home that wrapped his brand new set of headers before he went on a trip to the West Coast. He burned one tube out before he got half of the way to his destination. He told me that when he pulled the leaking header off the motor home, the first 4" off the head of one tube literally crumbled in his hand. WOW!

The speed of sound is related to the temperature of the medium in which it is traveling so coatings would have an effect but I think it would be minimal. However, I think you should concern yourself with the things that are really important about header design as coatings are not that important other than they be applied correctly so that they stay on.

Coatings are usually applied INSIDE as well as outside so the comparison to BBQ (Barbeque) paint wouldn't be correct as it is on the outside. Also - coatings are baked on while normal paints are not. You are trying to compare two different animals.

There is minimal design effort demonstrated in the header industry - certainly no one is considering that effects of coatings in the design of their headers as it is obvious they are NOT considering other elements of design that are much more important. Again, worry about what is important.

Thanks. Ed Henneman

Questions about designing a header BETTER than an existing header.

Dear Chuck:

Assuming that the tube length is near correct already, adding 6" of tube length will strengthen mid-range and bottom end power but will diminish top end somewhat. If the tube is actually too short, you might get a power gain over the entire rpm range of the engine! (But don't expect that to happen here.)

If you like what the current header does, I certainly wouldn't go any larger as that change can be more profound as to its effect which, in your case, would be to hurt bottom end and mid-range power MORE than it might help top end power (but the potential increase of top end power also ASSUMES that the engine might actually need a bigger header at high rpms - if it doesn't, you won't get a gain a high rpms going to a larger tube). In our own testing we have often seen total (broad rpm range) performance gains by going to longer header designs. That is why, in most cases, our headers are longer than others headers. (Keep in mind that many companies are run by "bean counters" who see a long header as a waste of material - just as they see an equal length header - due to its increased complexity - as a waste of production time. Their view point is based on production costs - not how engines actually perform with their products . Their marketing always stresses performance but the design of their products often don't.)

By the way, I don't think it is possible to "fool" an engine. You can fool people (that's called marketing) but, engines - that don't have brains - are often smarter than the people who own them. I've dealt with guys for over 40 years and am continually amazed as to how many I've encountered that are not able to think critically (and I feel that it's getting worse - possibly something in our water?). For example, I have watched guys switch headers (from some other brand to ours) and see the car run very much better afterwards yet others (who witness the car being faster so no one argues that) will argue that the header change did NOT make the car faster because they will accuse the customer of making other changes at the same time the headers were installed and those changes are why the car is faster (certainly NOT the headers as they apparently don't want to believe that we actually achieved a gain). For example, many times I have had my customers tell me that others INSIST that they changed camshafts at the same time that the headers were installed. We make the cars faster but get no credit for doing so due to the dysfunctional reasoning of these guys. (One thing that bothers me about the "cam" argument is that I've known guys that have switched camshafts and either didn't get a gain in the process or even slowed down because they found out that the cam they already had was a good or better choice. So why do guys argue that the "cam" is what made the car run better when that argument isn't even consistent in its own right?) Guys that own ______ headers are the worst of this group because, when they see someone switch from ______ headers to ours, they will argue until hell freezes over that any performance gain achieved was due to some other change or changes that the customer made simultaneously. They will NOT consider, in any way, that we might have actually come up with a better header design - one that actually matched BETTER the needs of the particular situation. That is why I consider many ______ header owners as often mentally dysfunctional - they will believe whatever they want to believe as facts are not important (UNLESS the facts support their point of view!). It always amazes me to see how one can make a better product - one that actually works better in a real world environment and guys witness the gain yet will argue about how it was accomplished. Think of the logic: A person makes one change. The vehicle runs better after that change. Isn't that change the reason why the vehicle runs better? Simple logic until guys are involved because many don't want to hear about what took place because it doesn't coincide with their beliefs - therefore, they are argue about - often denying their own vehicle a performance gain!!!! It's almost like arguing about religion (a system of beliefs) - facts become unimportant or irrelevant.

I would NEVER make two design changes in a header simultaneously as it becomes impossible to determine what change worked as well as to what extent it worked. In your case, going longer and larger at the same time, it might be possible to have one change cancel the other out. What a waste of time that would be if that happened.

One of the biggest problems guys have with headers is that there is very little experienced, objective discussion about header design. Most of the writers for magazines are not well informed and seem to reflect more what advertisers are trying to sell. They certainly won't "blast" somebody for building a lousy header (or any other product, for that matter).

I've dealt with motorcycle guys for years - but mainly Harley guys. It is amazing how many times these guys build headers of some sort and then come back about 2-3 weeks later to buy more parts but smaller than before - to build a second set of headers. They often express amazement as to the "damage" the larger headers created - rather than get a performance gain, the bike ran worse!

Besides running header tests and using other methods to gain "header" knowledge, we have learned a lot from customers over the years by just selling parts to them and getting the feedback from their efforts - but we don't see this type of discussion appearing in magazines either. Magazines are in the business of motivating people to spend money. Negative discussion - like discussing how some change HURT performance - is NOT what they are about. That is one of many reasons why I don't like magazines - they don't reflect what is actually going on.

Hope this helps. Looking forward to your Header Design InfoPak order.