Dynomax Exhaust System - CHP Insider

[Ed Blown Vert]

Dynomax Exhaust System - CHP Insider
At its core, an exhaust system is nothing more than a series of pipes that route toxic fumes from the engine to the back of a car. At least that's what they thought back when outhouses were still in style. Now, as advanced life-forms that take care of business indoors, we've gathered sufficient data that proves otherwise. Despite its perceived simplicity, exhaust-system tuning is a complex art that still baffles some of the top engine builders in the country. Minor variations in collector size, header primary length, and tubing diameter can significantly impact power output for better or for worse. To make sense of it all, we hit up Scott Stutler of DynoMax. In addition to explaining some of the science behind various exhaust theory, he offered some valuable tips on how to select the right components for your car, keep noise in check, and piece together a custom exhaust system that best suits your needs.
Collector Sizing
Collectors don't look like much, but they play an important role in exhaust tuning. Ideally, the collector diameter should be within 0.5 inch of the rest of the exhaust system. For example, on a 500hp motor with 1.875-inch primaries and a 3-inch exhaust, the collector should measure between 3 and 3.5 inches. "Shorter collectors produce peakier power curves and improved high-rpm performance, while longer collectors produce a broader power curve," Scott explains. "As a general rule, guys with open headers run header extensions to maintain a smooth transition from the four header tubes into the collector. Extensions give another 12-14 inches for exhaust pulses to transition and smooth out."
Equal-Length Primaries
The virtues of equal-length primaries make for great advertising propaganda and bench-racing discussion, but they're neither necessary nor practical in a street car. The goal with equal-length primaries is to tune the exhaust pulses by experimenting with different primary lengths. If done correctly, the exhaust wave will arrive at the exhaust valve right when it opens to maximize scavenging. "In reality, when you put each type of header on the dyno, the power difference between the two is negligible," Scott says. "In NASCAR or Pro Stock motors, where a 1hp improvement is considered a huge deal, having equal-length primaries is more important. However, you're splitting hairs by comparing headers with equal-length and non-equal-length primaries in a street application."
Sound-Damping Techniques
The two prevailing technologies in mufflers to reduce exhaust noise levels are through the use of chambers or by packing them with fiberglass. Each method has its pros and cons. Fiberglass mufflers work by converting sound waves into heat energy through absorption. "They're less susceptible to resonance than a chambered muffler design and typically flow better as well," Scott explains. "The downside is that the sound level changes as the fiberglass material burns up or melts, at which point it loses all damping ability. On the other hand, chambered designs won't burn out, but they produce a love-it or hate-it tone. We use both sound-damping methods in our Super Turbo muffler, which makes it unique."
Backpressure
Some people say a motor needs a bit of backpressure to preserve low-end torque, while others argue that the less backpressure you have the better. "The fact is, an engine does not need backpressure," Scott says. "What it needs is scavenging, which is directly related to exhaust velocity. A common misconception is that you'll lose some low-end torque by stepping up to a larger after-cat system. What's really happening is that the larger-diameter piping is moving the rpm range where the scavenging takes place higher up the powerband. Since exhaust velocity increases with rpm, you're not losing power but moving it higher up in the rpm band instead."
Resonators Vs. Mufflers
"Resonators and mufflers are similar, but not quite the same. Consequently, there is a time and place for both. By definition, mufflers and resonators are both sound-attenuation devices, so they're one in the same. However, by practice, a resonator is perceived as something round and compact, while a muffler is perceived as being larger and more substantial. Resonators reduce exhaust noise by 4-6 decibels, while mufflers reduce noise by more than 20 decibels, so the applications in which they are used can be very different. Resonators are small and light, so they're popular in racing classes that require some type of muffler. On the other hand, for street applications, using a resonator without a muffler typically emits more noise than people care for. If someone is having a problem with resonance, a practice becoming more popular is installing one resonator or multiple resonators in addition to a muffler, which can reduce resonance enough to where it's no longer noticeable. Our Bullet mufflers are used very often for these types of applications."
Mandrel Bends
It's almost universally accepted that mandrel bends are superior to crimped bends, but just how much better are mandrel bends over a very well-done crimp job? Typically, you'll see a 20 percent reduction in the inside diameter of a crimped pipe compared to a mandrel-bent pipe. "If you're mandrel-bending a 2.25-inch exhaust, it will flow as well as 2.5-inch inch crimped bend," Scott explains. "If someone wants to run 2.25-inch pipes with crimped piping, then they should step up to 2.5-inch tubing. A mandrel bend is as close as you can get in flow to a straight pipe."
Case Size
The physical dimension of a hot rodder's muffler choice is often dictated by the amount of space available beneath a car. However, the size of the muffler case can also affect how well it flows, so there's more to consider than just packaging issues. On a straight-through muffler-one that does not use internal baffles or deflectors-the size of the muffler case will not affect flow. In a chambered muffler, case size can affect flow depending on how the reflectors are arranged. "In general terms, the shorter the muffler the better the flow, and sound is greatly impacted by case dimensions and by shape as well," Scott says. "Although oval mufflers have a tendency to resonate, they are typically quieter than round designs. Also, a longer case usually results in a quieter exhaust."
Cats
Whether you choose to or are forced to run cats, aftermarket units are almost guaranteed to flow better than factory hardware. It's not necessarily due to differences in quality, but rather longevity. An OE converter has a higher volume of precious metals, and therefore larger bricks, since they're designed to last more than 100,000 miles. "In an aftermarket converter, the brick is smaller because federal law requires manufacturers to warranty it for only two years," Scott explains. "The smaller the bricks the better the flow and easier the installation. An aftermarket cat will typically flow 5-15 percent more than a factory cat."
Resonance
"Most people don't mind a loud exhaust but can't stand resonance. Nine out of 10 times, people have resonance problems because they don't have a balance tube in the exhaust system. An H-pipe is good, but an X-pipe is better. If you're still getting resonance with a balance pipe, the next step is using an absorptive muffler instead of a chambered muffler. This may increase the overall sound level, but the resonance will decrease. If that's still not enough, using resonators can reduce sound level enough to where the resonance isn't noticeable. The best way to route tailpipes is to have them exit straight behind the car. Turndowns direct sound waves toward the ground, which will bounce them off the pavement and rattle your floorpan."
X-pipes vs. H-pipes
A balance tube is absolutely essential to a good exhaust system, and you're leaving power and fuel economy on the table without one. Both X-pipes and H-pipes get the job done, so which is better for your car? "An H-pipe is pretty easy to incorporate into an existing exhaust system, and in cars with a tight chassis like G-bodies, an H-pipe is easier to install," Scott explains. "X-pipes are superior to H-pipes because they provide a smother transition from bank to bank for exhaust gases exiting the ports. Due to this reduction in turbulence and sound waves, X-pipes yield increased flow and a reduction in noise."
Header Design
"It's a well-known fact that long-tube headers are superior to shorty headers, but there's more to the equation than just primary length. A shorty is usually just a copy of a factory manifold that happens to flow a little better. Since exhaust velocity coming out of a port can reach 700 mph, it will go through pretty much anything that's close to the port. Long-tubes, on the other hand, are designed with exhaust velocity in mind. With long-tubes, not only do you improve flow, but you're also moving the powerband by changing the scavenging effect of the exhaust. For instance, if a motor has a sweet spot at a certain rpm range, you match primary length to maximize scavenging at that sweet spot and see a significant improvement in performance. In the best-case scenario, every header would be tuned to maximize scavenging for each engine, but that's not realistic from a cost perspective."
Noise And Flow
If you're looking for a whisper-quiet exhaust that offers maximum flow, then you're out of luck. Although manufacturers are always trying to find a balance between flow and noise output, the more a muffler flows the more noise it will emit. "An OE muffler uses containment technology, which is very restrictive and traps sound waves," Scott says. "The byproduct is that it also contains the exhaust instead of letting it flow through the muffler. By increasing flow through reflection, refraction, and absorption, noise output will increase; fortunately, there are hundreds of mufflers on the market to suit all applications and tastes."
Manufacturing Process
"Something most people don't realize is that Dynomax is part of Walker, which is one or largest OE exhaust suppliers in the country. The benefit to us is that when there's a new car on the market that may sell 300,000 units per year, all the technology that allows us to produce exhaust systems in such high volume to such exacting standards goes into our aftermarket systems as well. Our fixtures, jigs, and tooling are unparalleled, and we have far more data points than most competitors. That's one of the keys to why our products fit so well. Being an OE supplier also gives us the ability to come to market quicker with new products when a new vehicle platform is released."
Underhood Heat
Using ceramic coatings is one of the best ways to reduce underhood temperatures, but there are other effective techniques to consider. "Outside of coatings, header wrap works best at reducing heat, but it also retains moisture and causes rust," Scott explains. That said, most people who run turbos use header wrap extensively, so it's definitely effective. "Header boots are another alternative, which cover just the critical areas and are easier to install. High-temp plug wires and shrouds can also be used to protect important components such as brakes lines and starters. Even with coated headers, maintain at least a 2-inch air gap between the headers and other components to allow sufficient heat dissipation."
Power Adders
For any given power output and displacement, a generic sizing chart can get you in the ballpark when choosing exhaust-pipe diameter. However, engines equipped with power adders have a different set of needs. "If you're running a turbo or supercharger, there's really no such thing as an exhaust that's too big," Scott explains. For forced induction, the bigger the better. "In a race application on a nitrous motor, the exhaust should be built in respect to the max horsepower it makes on the bottle. Conversely, in a street application with nitrous, the exhaust system should be built in respect to the maximum horsepower the motor makes off the bottle. That way, you'll optimize the exhaust system for the operating conditions that the engine sees the most."

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[jimmybling31]

I liked that. very imformative.

[Tyler_LS1]

that's some good info

[Tnhillbilly]

Doggone good info in this read! Thanks, Ed

[aerojt]

Best read yet

[Y2KArcticSS]

does dynomax make decent exhaust systems for f-bodies (possibly a stupid question, too lazy to find out for myself )

[fxgs]

Great info..........thanx......saved in "My Favorites"

[lilpb1]

Good info.

[blackcamarob4c]

That should answer alot of questions!! It did for me. Thx for that post.

[Smokeybrnout]

Wow, I didn't realize this was on this site. Thanks for posting Ed. I am no longer with DynoMax, but they do build good systems for F Bodies. I now work for the Stainless Works and have moved back home to Northeast Ohio.

[hamburger68]

does dynomax make decent exhaust systems for f-bodies (possibly a stupid question, too lazy to find out for myself )

i run a 3" dynomax catback, i like it. choice of two mufflers, the "super turbo" is a very deep sounding muffler, i have the "ultraflow" which it more open sounding.

[levityinc3]

A few questions, as I am about to purchase the TSP True dual Rumbler (or something comparable), and long tubes. What is scavenging, in terms of back pressure? I take it to mean how adequately the exhaust gases are extracted from the motor and out the back of the vehicle. Therefore the theory of opening flow and reducing back pressure will still transfer your torque numbers to the higher end. Are there dyno sheets of a stock LS1 vehicle versus an LS1 vehicle with only long tubes , an X-pipe, and a tune (maybe air intake also)? I ask because I am wondering if you can increase scavenging while keeping the torque numbers in the same power band by using a smaller diameter pipe, in the same configuration as the previous setup; or will that simply increase back pressure also?. And what exactly is resonance? I don't take it to be, simply, a component in the exhaust system vibrating; or am I over-thinking it?