The Science of Exhaust: Expert Education from Burns Stainless
Many of us recall our very first vehicle modification, which likely consisted of installing an aftermarket exhaust and maybe even headers. For many enthusiasts, as time progresses, the desire for more speed and horsepower often leads to the next level of modifications, which include dipping into the engine and equipping it with high compression pistons, larger duration/lift camshafts, or maybe even forced induction.
But most don’t think twice about going back to address the exhaust system which was installed before making those major modifications. Once more powerful modifications exist underhood, it should be considered. The engine’s horsepower levels have dramatically increased over time, yet the exhaust remains the same from day one.
“That’s a common scenario we see at Burns Stainless. When talking with customers, they often reveal they installed a header over 15 years ago but never upgraded it regardless of the changes that were made to the engine,” says Burns Stainless owner and head engineer Vince Roman.
“As an engine builder, you need to look at the entire engine package as a whole and try not to focus on one specific aspect of an engine. You want your high-powered engine to breathe more efficiently, and a byproduct of that efficiency is more power. Think of it this way: you wouldn’t spend big money porting your cylinder heads, just to end up reinstalling a stock carburetor, right?”
With clients ranging from Formula SAE, NHRA, and IMSA to competitive tractor pullers, Burns Stainless has earned its experience in the motorsports industry over the last 30-plus years.
The company was founded by Jack Burns back in the 1980s. A typical California car enthusiast, Burns enjoyed working on cars and often competing at the local drag strip. His love for speed started at an early age, and he eventually moved on to working full time at S&S Headers as a fabricator, until he decided to open up his own shop, Burns Fabrication. Early on, the company focused on building race boats, where Burns began perfecting the performance and design of the merge collector. Burns is also credited as a pioneer with using stainless steel for exhaust headers and collectors, a material rarely used during that time for high-performance automotive applications.
“What really separates us from everybody else is the quality and craftsmanship that goes into each and every collector we fabricate and sell. Every piece is touched by Burns, as he currently manages the fabrication shop and prototyping department. He will sit there and quality-control every piece prior to it leaving the shop. That says a lot about the passion he puts forth into the Burns Stainless company name,” says Roman.
“Depending on the type of motorsports our clients campaign in, whether it be road racing or drag racing, we offer various-sized collectors, as well as customized exhaust pieces according to exact performance applications,” says Roman.
Burns Stainless has developed its X-design program, a parametric exhaust system modeling computer program. This program offers numerical outputs predicting optimal header and collector dimensions custom-tailored to the customer’s needs for flawless exhaust tuning.
X-design uses specific engine algorithms incorporating engine bore, stroke, and compression ratio along with camshaft and cylinder head dimensions to render detailed specifications of the ideal exhaust system parameters. Depending on the engine builder’s goal, the X-design program can render a 4-into-1 and a 4-2-1 system. A six-cylinder engine can be modeled using three possibilities: 6-2-1, 6-3-1, and 6-into-1, and the program is also optimized for V8 applications as well. The best part of the X-design program is that it is included with the purchase of a Burns Stainless Merge Collector.
Once the form has been completed, Burns Stainless will make the proper calculations then contact the customer typically within two days to further discuss horsepower goals and make the necessary adjustments to the designs. Then, the data is finalized and a design sheet is printed—along with a parts list—so the customer can fabricate their custom header or headers. Burns Stainless provided us with a sample printout of a LS7 4-to-1 stepped header transitioning into a 3.5-inch collector.
“We’re excited about offering our X-design program. Sure, there are computer software programs you can purchase, or online calculators, but I find them not detailed enough to give you the right information. Or the analysis is left up to the user to extrapolate a bunch of numbers that often don’t mean a lot unless you really know how to apply them. That’s where we come in,” says Roman.
The intricacies involved in developing a Burns Stainless header are on full display in this NASCAR Cup Tri-Y header.
“We don’t make any production headers; each and every set is custom,” says Burns. This header uses a stepped design with a smaller primary pipe starting from the base of the cylinder head that replicates the port size. As the runner length continues down towards the merge collector, the pipe steps to a larger diameter. This stepped design allows the gas velocity to remain high near the port with a stepped-up pipe to reduce velocity drag. The stepped design also allows for pressure wave reflections which travel back up the pipe and are presented at the exhaust port.
As the exhaust pressure wave arrives at the end of the exhaust pipe, part of the wave is reflected back towards the cylinder as a negative pressure (or vacuum) wave. This negative wave, if timed properly to arrive at the cylinder during the overlap period, can help scavenge the residual exhaust gases in the cylinder and can also initiate the flow of intake charge into the cylinder. If a header has been improperly designed, the same waves at a specific tuned rpm can backflow at the wrong time and cause disruption, which can cause a loss in power potential or performance. Roman states that stepped designs are not a gimmick—it’s a concept that has been proven to work and is associated with proper engineering.
Many performance enthusiasts have watched Engine Masters Episode 4 online where the crew takes a sledge hammer and proceeds to bash a header’s primary tubes nearly flat. The premise behind their hammer-time extravaganza was to test the concept of whether “massaging” the exhaust tubes to fit power steering pumps or other devices would cause a loss in horsepower. Surprisingly, the 400 cubic-inch engine was dyno tested before and after the bashfest with little to no loss in power.
When asked about this, Roman replied with five simple words, “The header was too big.”
He says one of the largest errors street enthusiasts make is to run too large of a primary pipe, and too large of a collector. “Now if they used a properly-tuned header and proceeded to hammer away, I would guarantee you they would have experienced some serious horsepower loss,” he says.
Off the Shelf Headers
“We understand why people end up buying a simple bolt on system. It all comes down to cost and convenience. On the flip side, someone might take these off-the-shelf headers and throw them on an LS7 while another guy uses the same headers and slaps them on their LS3. You can’t take something that’s designed for one specific application and throw it on multiple vehicles assuming it will work. No two engines are the same and to say that one specific header is the answer to all isn’t justifiable,” Roman explains.
B-TEC Tunable Exhaust Collector
Many top running NHRA Pro Stock, Super Stock, and Comp cars use this setup. The megaphone design works by allowing gases to expand at a controlled rate coming out of the final collector.
Burns Stainless recommends using a megaphone to broaden the power peak for vehicle applications that do not use tailpipes. A megaphone designed with a reverse cone delivers maximum peak horsepower and power bandwidth.
The company also offers an adjustable megaphone which allows the engine builder to fine-tune an exhaust system while experimenting with different cams and engines. The collector outlet uses interchangeable venturis, which slip into receivers directly behind the collector.
“The adjustable megaphone allows the tuner to dial in their horsepower numbers on the dyno using different outlet sizes, ranging from the smaller size for more mid-range power to the larger size for more top-end gains. The X-design program allows engine builders to determine what would be the best application for any particular setup,” says Roman.
Burns mentions that some individuals refer to the material called Inconel as a “super stainless.”
“Inconel is in the same family as stainless steel, but it has a higher Nickel and Chromium content, and can handle more heat. For turbo applications or rotary engines which typically see high exhaust temperatures, we recommend using Inconel,” he explains.
Burns mentions he doesn’t want to use tubing which is too thin. The idea is to build an exhaust manifold or header that is both strong and durable using 16- or 18-gauge tube thickness.
“The cool thing about Inconel 625 is it doesn’t have the thermal characteristic commonly associated with stainless steel which rolls, contracts, and expands with heat,” says Burns.
“The thermal properties of Inconel are graded slightly less than mild steel. Most importantly, using Inconel will eliminate the constant issues of exhaust primary pipes or downpipes from pulling things apart when continuously heat-cycled. Although expensive, Inconel collectors are commonly requested by our customers. Using 625 Inconel allows us to use a much thinner wall thickness pipe that’s lightweight.”
During our conversation, Roman—the typical engineer—wanted to double check his facts by quickly pulling out a large binder filled with hard data. When it comes to headers and exhaust design, these guys don’t mess around!
Titanium Grade: Superior Quality or Inferiority?
Over the years, Burns Stainless has seen a number of customers walk into their shop hoping to repair their damaged titanium header they purchased elsewhere.
“A common scenario would be these motorcycle guys stroll in with cracked headers they want us to repair. We make the repairs and low and behold they come back to us after a few months with the same inferior quality header cracked in an entirely different location,” says Roman.
Burns Stainless fabricates their titanium headers and collectors using CP2 grade material. CP2 is known as Commercially Pure Grade 2 Titanium, which comes in the annealed condition (heat-treated to increase ductility and reduce hardness) and has moderate strength and excellent resistance to oxidation and corrosion. It is used in a variety of industries such as chemical, marine, medical, recreational, and aerospace.
“CP2 has the properties that allow us to cold bend the material. Any lesser grade or material would be too brittle,” says Burns.
Burns Stainless prides themselves not only on their craftsmanship, but also the material used with every part produced by the company.
All of the stainless steel products are fabricated using 304L Stainless. The “L” represents low carbon, which translates to higher temperature properties and improved corrosion resistance over standard 304 Stainless. 304 Stainless can sustain temperatures up to 1,400 degrees Fahrenheit, while 321 Stainless is good up to 1,800 degrees. Anything above those heat numbers call for Inconel for durability reasons.
Burns Stainless typically doesn’t stock titanium or Inconel merge collectors. Customers that do request these products typically require custom fabrication. Burns mentions that they do stock what they refer to as a raw collector to provide a quicker turnaround time.
The man, the myth, the legend—Jack Burns—is all smiles while he holds up a Burns Stainless Megaphone with optional reverse cone welded to a 4-to-1 merge collector.
Nestled deep inside the storage room, we found a Corvette ZO6/ZR1 prototype exhaust using 18-gauge 304 stainless steel 3-inch piping. This exhaust system not only improves performance but also sheds 35 pounds from the factory exhaust system.
“This exhaust really wakes up the car and gives it a distinct exhaust tone, similar to the ALMS GT2 Pratt and Miller Corvette Racing program, which we had the pleasure of working with and engineering exhaust systems for,” says Roman.
Burns Stainless also offers a two stage muffler that was engineered with an absorption muffler in the first chamber and a Helmholtz-type design that is comprised of baffles in the second chamber.
While taking some photos of the compact race exhaust muffler, we immediately noticed the baffles. Roman explained that the baffle design is comprised of holes smaller than those typically used by competitors. This design offers improved exhaust flow with less restriction.
Burns Stainless exhaust systems are rebuildable, and are available using three types of packing material ranging from glasmat fiberglass to stainless steel depending on the vehicle’s application.
Modified production style drag race 4-into-1 collector with a Burns Stainless Ultralight Motorsports muffler. This tuned collector package comes in at a flyweight 3.5 pounds.
All exhaust components are machined and hand-fit in house. Collectors are purge TIG-welded and internally blended.
The internal blending process give a smooth transition for exhaust flow and improved performance. While the process is more time consuming, Burns Stainless states this is what separates their products from the rest.
Gases moving through the exhaust pipe do 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.
This 8-into-1 merge collector is popular among the V8 community, including off-road vehicles and trophy trucks. The distinct Gatling gun sound that the 8-into-1 emits is more than enough reason to install one, but Roman doesn’t recommend using this type of merge collector for street-driven vehicles.
We sincerely appreciate the invite to check out the Burns Stainless facility, and hope you enjoyed this look behind the scenes.
Motorsports Photos provided by Burns Stainless