I first met Jack Burns about ten years ago. At that time, I was working over cylinder heads for Trans Am, ASA, and BGN series engines at a great shop called CRD Engineering. Jack was experimenting with header designs for the Trans Am series, and he'd occasionally bring a pair of his pipes over for testing on our dyno.
What struck me about Jack was his intensity. He'd pull up in a tired old Chevy van, slide the side door open, and break out these tubular works of art he'd crafted. He'd share his ideas and theories on improving power, and many of his pipes showed up on winning cars.
I moved on from CRD when they relocated to North Carolina to focus on NASCAR interests, and didn't see Jack again for quite awhile. When I did, he was creating headers for both NASCAR Winston Cup cars and NHRA Pro Stockers.
While Jack and I have both evolved from where we first met, we're both still focused squarely on what we love. I wanted to introduce my readers to Jack Burns, and have him share some time-tested exhaust theory with you. Jack lives in a "header-centric" world, where optimal header design is paramount and everything else should be designed to work around the headers. Of course, this cannot be reality for all of us, but look over what Jack has developed, and enjoy a tech article that's been ten years in the making.
When it comes to headers, like all other engine parts, compromise is the order of the day. When designing custom exhaust headers, the task of minimizing these compromises is paramount, and only by focusing on each individual portion of the header can an optimal design for the specific task be created.
At Burns Stainless, the determining factors for optimal performance in any application have been heavily researched and developed into a computer program to speed the development of header design. While this software is proprietary, Jack was kind enough to share with us many of the critical factors embedded into the software. By sharing these facts, Jack hopes to educate street enthusiasts on the critical points to consider when shopping for headers. If readers are able to qualify their purchases using Burns' theories, a more prudent and effective purchase can be made. Knowing what dimensions you're looking for should play a heavier role in deciding which headers are best for you, even over budgetary considerations. We're in this to make the best power we can from our powerplants in the rpm range we most need that power to work for us, and by doing the homework prior to committing to a purchase, street enthusiasts should be able to get the most bang for their buck.
The header is created from a basic collection of parts, including the flange, primary pipes, secondary pipes (in Tri-Y headers), and collectors. While different header designs may carry different components, these basic parts can be looked at individually. Jack told us: "For just about everyone running an American V-8 on the street, the Tri-Y design is almost always optimal for overall power production."
Jack's Tri-Y design pipes are favored by road racers and NASCAR Winston Cup teams, in addition to many of the top NHTA and IHRA Pro Stock engine builders. One of the largest errors street enthusiasts make is in running too large of a primary pipe, and too large of a collector. For example, NHRA and IHRA Stock teams using Burns' headers in H/SA in traditional small-block powered musclecars are running 1.5-inch diameter primary pipes- much smaller than many street machines are trying to use.
"The purpose and rpm range of the engine determine the primary pipe length, while pipe diameter is governed by engine displacement, valve diameter, and valve curtain area (determined by camshaft dimensions). The exhaust port design is critical in determining the size differential and placement of steps in a step header, and since we create our headers individually on a case-by-case basis, we can create truly optimal headers. We don't make any production headers; each and every set is custom."
It should be noted that Burns Stainless usually provides design details and merge collectors to header fabricators, leaving the actual header building to them. Burns charges $75 to produce a complete header system design, but this charge is included in the purchase price of one or more of their merge collectors. Because of all this, we've decided to list the factors contributing to each portion of the header design.
PRIMARY PIPE DIAMETER FACTORS
The primary header pipe diameter is determined using basic engine mechanical specifications, such as: Bore Stroke Compression Ratio Valve diameter Cam specifications (lift and duration) Target rpm range
PRIMARY PIPE LENGTH
"The overall length of the primary header pipe is governed almost exclusively by the target engine's rpm range, which is dependent upon wave tuning. Typically, a lower engine rpm range likes a longer primary pipe, while a high rpm engine prefers a shorter primary."
SECONDARY PIPE DIAMETER
While typical off-the-shelf street 4-into-1 headers do not have secondary pipes, Burns' research has proven repeatedly that his Tri-Y designs make more overall power over a broader rpm range. While traditional lines of thought have street enthusiasts knowing Tri-Y pipes make more bottom-end torque, further research by Burns into the design have resulted in headers making more power all across the rpm range. With more components as part of the Tri-Y design, more tuning possibilities exist, and therefore more potential lives within.
"The secondary pipe diameter is determined by considering both pressure waves and reflective waves throughout the system. Since the pipes are paired according to the firing order, these waves can work together or against each other. Naturally, our designs work with the waves to increase the efficiency of the header, using the wave pulses to help pull gases from the engine.
"There are two basic kinds of waves we're dealing with. First, there are pressure waves. The pressure wave travels the length of the primary pipe in a 4-into-1 header, then is reflected from the collector where the area changes from the small-diameter primary into the larger-area collector. A reflection of negative pressure goes back up the primary pipe.
"In a Tri-Y design, the pressure of additional area changes (where the primary pipes become secondary pipes) produces additional reflections, so the Tri-Y must be designed in a different manner with respect to wave control. Given this, the area of the Tri-Y header between the first and second collectors becomes critical, and tuneable. The entire header is affected by this crucial length of pipe, and can be fine-tuned accordingly through proper sizing for optimal broad-range performance.
"The 4-into-1 pipe is also affected by altering pipe lengths, of course. But, without these secondary pipes it is impossible to tune with the same level of precision as with the Tri-Y headers. It's for this reason we prefer the Tri-Y design in most applications. The tuneability is so much more accurate, we're able to find more power over a broader rpm range. This is especially critical in engines expected to work well over a wide rpm range, like street machines."
Another huge reason for the move to Tri-Y headers is weight savings. Burn's claims most of their Tri-Y headers weigh in at about _ the weight of comparable 4-into-1 pipes for the same application, due to the smaller pipe diameters used throughout similar applications. Also, with less internal volume than comparable 4-into-1 headers, the Tri-Y equipped engine is typically more responsive. Tri-Y designs require physically smaller collectors as well, contributing further to space and fit concerns, and adding further to crisp engine responsiveness.
"There is much power to be found in researching collector design and size. The optimal collector is determined by several variables, and it's engineering interacts with the entire exhaust system. The internal volume, the outlet size diameter, and the angles at which the pipes come together within the collector are all factors that must be maximized for the header to perform to its full potential."
1 - Primary Pipe Entry Size
"Our computer model design program determines many of these hard dimensions based on data gathered over many years, including the length and diameter of the primary or secondary pipe entering the collector."
2- PRIMARY PIPE ENTRY ANGLE
"The pipe entry angle is typically between 10-20 degrees, with most pipes being right at 15 degrees. The cone (or goilet) formed between the pipes as they transition from primary to collector is formed as a consequence of these angles, nothing more. The mass of gases moving through the pipe does not want to change direction, so keeping these "pyramid" cones true to the pipe entry angle helps smooth the transition from the relatively small volume of the feed pipe to the larger volume of the collector."
3 - COLLECTOR OUTLET DIAMETER
"The collector outlet diameter is the most critical dimension in the header. It's what makes the merged collector work the way it does. Each collector we sell is custom-sized to each customer's engine, and there's no real 'formula' to get a broad-based general determination for street machines. As a rule, the overwhelming majority of aftermarket headers designed for the street market have way too big of a collector outlet diameter. Most street guys are losing power because of badly designed, manufactured, or engineered street headers. There is much room for improvement here."
4 - OVERALL COLLECTOR LENGTH
"Overall collector length is not critical. Once the other variables in the header design have been determined, the collector ends up being as long as it needs to be. We've found no benefit in lengthening or minimizing this dimension. It's more important to properly engineer what's going on inside the merged collector, and let the length determine itself once all the other important factors are optimized."
AFT OF THE COLLECTOR
One of the growing areas of research at Burns is the critical area just aft of the all-important collector outlet. Burns' dyno research led him to begin experimenting with interchangeable venturis, which slip into receivers just aft of the collector. While these prototype dyno parts were initially crafted to assist Jack in determining the critical overall collector diameter size, he soon realized they could be a marketable product. His initial "DynoSYS" product for dyno research evolved into a line of interchangeable sleeves called the Burns Tuneable Exhaust Collector, or BTEC for short.
The BTEC system has shown capability to alter the entire power curve of the engine. By changing only the insert, racers can change the entire tune on their engines to fine-tune for track conditions, weather, or driver preferences. Mostly used by drag racers, many in Pro Stock, the BTEC system offers enthusiasts a glimpse into the future of header design. While the drag racers have already embraced the benefits of BTEC, a number of road racers are beginning to experiment with the system as well.
Burns is also working with stealthy reverse-cone megaphones, which perform a similar task. While much information regarding the use of his reverse-cone megaphones remains secret, street enthusiasts should understand the use of these products is still primarily confined to open (unmuffled) exhaust systems. Therefore, there is little to be gained at this point in time from digging deeper into the design. In the future, products like this may impact the street market, but at this time they are purely race-only parts.
One area street machine enthusiasts are aware of is the evolution of the X-pipe. Early on, connecting the left and right halves of a true-dual exhaust system with an H-pipe resulted in measurable benefits. This theory evolved into the X-pipe, which allowed both left and right portions of the exhaust system to share some common flow area and resulted in even greater gains in power with a notable reduction in exhaust noise. This win-win situation prompted Burns to research even further, and his X-pipe designs stand among the finest and most-effective in use today.
Here's a look at a typical NASCAR Winston Cup header, as designed and manufactured by Burn
"Our X-pipes are designed for maximum inertial flow, and unlike other X-pipe designs, exhaust flowing through our X-pipe sees a minimal direction change. By minimizing the entry and exit angles of the X-pipe, we were able to limit the restriction through the unit, and find more efficiency. Exhaust flow does not like to change direction, so this is only logical.
"Most of our race customers still do not use X-pipes, but interestingly most of the NASCAR Winston Cup teams use them in their restrictor plate cars. For a street enthusiast, they are highly recommended."
WHICH STAINLESS TO USE?
Within the 300 series of stainless steels, there are four types that are suitable, available and cost effective for the racer. These are 304, 316L, 321, and 347.
321 and 347 are known as stabilized grades of stainless. These are alloyed with either titanium (321) or columbium (347), both of which have a much stronger affinity for carbon than does chromium at elevated temperatures. This eliminates carbide precipitation leaving the chromium where it belongs for corrosion protection...remember our discussion of intergranular corrosion? Both 321 and 347 are top choices for exhaust headers, especially turbocharger systems and rotary engines. Since 321 is much more available than 347, that leaves 321 as the first choice, with no sacrifice in needed qualities.
316L is an extra low carbon (ELC) grade of stainless that has only .03% carbon, making less carbon available to precipitate with the chromium. It is used extensively in marine exhausts where salt water corrosion mixed with diesel exhaust particulates and electrolysis create such a horrible environment that even other grades of stainless cower and run away!
304 is the most inexpensive and available stainless in the 300 series. It is suitable for normally-aspirated header applications, and has been successfully used by many racing teams. It does not have the high temperature fatigue resistance that 321 does, but is considerably less costly and much more available. Most 304 tubing these days has the dual designation of 304/304L.
Practically speaking, there are overlapping applications of 304 and 321 stainless in header construction, but knowing you've got the insurance of the aircraft-grade 321 for the job is definitely worth consideration of the extra cost... if your application requires it.
Stainless steels come in both tubing and pipe sizes. Since certain pipe sizes are almost identical in dimension to tubing sizes, pipe may sometimes be substituted for tubing, and vice versa. Numerous wall thicknesses are available, but for headers, normally .049" (18-gauge) to .065" (16-gauge) is used.
Different specifications are used to meet particular requirements for the military (MIL), the American Society of Testing Materials (ASTM), and the Society of Automotive Engineers (SAE). Examples of what to look for when you order stainless tubing are as follows:
ASTM A-554 304 stainless is a welded mechanical tubing used primarily for ornamental purposes. It is not fully annealed and is work-hardened slightly in manufacturing. It has good column strength and good bendability. ASTM A-269 304 stainless is a general service commercial specification that is higher quality and is fully annealed for better ductility. It is available in both welded seam and seamless, and is a good spec for the racer to use. We have not seen any difference in longevity between welded seam and seamless stainless tubing in header use, but there is a substantial cost difference. The column strength is not as good as A-554, but it has excellent bendability with a higher cost due to the full annealing.
MIL-T-8808/8606\MIL-T-6737 321 stainless are military specifications for aircraft tubing. Suffice it to say that some MIL-specs are not necessarily better or even as good as some ASTM standards. There is no particular magic here.
There are as many uses for stainless steel as there are projects in the shop. There is nothing else that transmits an image of quality and skill to the majority of fabricators than a cleanly constructed stainless steel project. Whether it is a set of headers, intake stacks, or even a stand for one's dyno engine cooling fan, stainless steel has such great mechanical properties that its use should be considered for many projects beyond exhaust systems.
|Material Properties||Aluminum 6061-T6||Aluminum 6061-T0||Mild Steel 1010 Crew ||304 Stainless Annealed ASTM A269||321 Stainless Annealed||TTitaniur CP2 Grade 2|
2ASTM B 338
lb/in2 (70 F)
lb/in2 (70 F)
|Modulus of Elasticity|
x 106 lb/in2
in/in-F x 106 ( 70 F )
BTU/ft-hr-F ( 70 F )
A GREAT SET OF HEADERS CAN MAKE ALL THE DIFFERENCE
Brenda Grubbs of Orchard Park, NY, has taken full advantage of Burns' header products under her H/SA '69 Camaro, which is powered by a Woodrow Josey-built 350 backed by a Turbo Action Powerglide. Currently, Brenda's best elapsed time is 11.39 at 116 mph.
Her header story is one not soon forgotten. In hammering through the rounds at the 2001 Holley Springnationals, the new headers had arrived but had yet to be installed. Entering the third round of eliminations, she had to face another class car, meaning the race would be run heads up. Brenda had been running a tenth and a half slower than the other car all weekend. Normally, this would be the last time anyone would consider changing anything under a Stock-class racer, but if the headers were going to be worth any ET, now was the time.
"After changing the oil and altering the shift point slightly, we decided to put the new headers on. We had no idea what the headers would do for us, but we had nothing to lose. As I waited in the staging lanes, people stopped by to give their condolences and joke about how I should use some nitrous. While I was seething, I just smiled.
"When the lights came down, I nailed a .517 light to his .540, and when we went through the lights I posted an 11.413 to his 11.403, and we got the win light. We'd never run faster than 11.61 prior to installing the headers. They were good for approximately 11 hundredths, have been on the car ever since."
Brenda's headers were fabricated by Elston Exhaust using Burns' components. They made all the difference for her, and improved the performance of the car tremendously. Brenda won every heads-up race she ran in both 2001 and 2002, and she captured the 2002 IHRA Stock World Championship by winning both the Holley Springnationals and Carquest Auto Parts Empire Nationals.
"While I've been blessed with a lot of accomplishments running in the Stock class, that round will always hold a special place in my heart."
The Tri-Y header design teams up cylinders on opposite sides of the firing order as much a
All portions of Burns' headers are hand fabricated and hand welded. It's this level of cra
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Varying sizes of venturi insert can be installed behind existing header collectors using B
These tuning aids offer customers the option of fine-tuning their power and torque curves
tuneable insert may represent the future for the aftermarket header industry. We can't wa
Dyno and track testing with different sizes and styles of venturi has shown fairly remarka
Many owners of lowered vehicles are choosing to run oval-shaped tubing for additional grou
For a snug-fitting big-diameter system destined for life under a ground-hugging street mac
As we mentioned, each portion of a Burns header is custom-designed and built. Here we see
This is how NASCAR Winston Cup headers get made. The complete mock-up long block is sent d
Here's the passenger side of the same engine. In addition to crafting optimally-designed h
I hope you've enjoyed meeting Jack Burns and seeing his amazing work. I'm proud to have sh