Exhaust System Guide –
Exhaust System Overview
• How the Exhaust System Works
• Importance of Correct Back Pressure
• Replacing the System
Exhaust System Basics
Exhaust System Components
• Stack Pipes
• Exhaust Clamps
• Rain Caps
• Heat Guards and Grab Handles
• Flexible Tubing
Over the years, the exhaust system has been given more responsibility and its job has grown. Originally, it was a relatively simple duct system designed to prevent toxic exhaust gases from entering the driver’s cab. Today, the modern diesel exhaust system reduces noise and even lends a hand with increasing a vehicle’s fuel economy, power and overall drivability.
Yes, it’s another story of change. Changes throughout the industry. Changes in governmental regulation. Changes in consumer demands. In the United States during the past 30 years, federal, state and local governments have introduced noise pollution control. The Federal Noise Control Act of 1972 was the first nationwide law to regulate truck noise levels. This regulation, which first went into effect in October 1975, limited total truck noise levels to 86 dB(A), measured at
50 feet (15.24 m) for speeds less than 35 mph (56.35 km/h). In January 1978, this noise level was reduced to 83 dB(A); followed by another reduction in January 1988, when the noise level regulation was lowered to the current 80 dB(A) level.
According to Australia design rule 28/01 in 2006, noise regulation is based on a different testing method. The sound measurement is taken at 24.61 feet (7.5 m) for speeds of 31.07 mph (50km/h). Depending on the vehicle’s horsepower, the sound requirement ranges from 81-87 dB(A) for heavy goods vehicles. In Europe, the noise regulation has been updated many times since 1970. The latest amendment was June 6, 2007, which specified that for heavy duty trucks with an engine horse power of not less than 150 kW, the noise level can not exceed 80 dB(A) measured at 24.61 feet (7.5 m) for speeds of 31.07 mph (50 km/h), according to Directive 70/157/EEC.
In China, for trucks with an engine over 150 kW produced after January 1, 2005, the noise levels can not exceed 84 dB(A). The sound measurement is taken at 24.61 feet (7.5 m) for speeds of 31.07 mph (50 km/h). Besides the noise, other by-products of engine combustion are exhaust particles and gases emitted into the exhaust system. Legislation to control the levels of these emissions occurred in 1988, 1990, 1991, 1994, 2004, and 2007. Each regulatory change reduced the acceptable levels of combustion-related gases which could be allowed to exit the exhaust system.
To meet these emission laws, Nelson Global Products works closely with all engine and truck manufacturers to provide exhaust system components. As the global leader in exhaust design, Nelson Global Products develops and provides highly specialized exhaust systems that reduce noise and minimize harmful gases.
Five Ways to Reduce Noise Levels
There are five primary sources that contribute to the noise level of a highway truck.
1 – Fan Noise
Excessive fan speed is a common contributing noise source. This can be controlled by the use of a temperature controlled or thermostatic fan. Other noise concerns are bent fan blades and broken or missing shrouds.
2 – Air Intake
Both the type of system and the location of the inlet affect the truck noise level. Air inlets that open to the side are generally noisier than those that do not. Intake air silencers are available for problem applications.
3 – Mechanical Noise
The engine and drivetrain are also a source of noise. Operating speed, type of engine and drivetrain all affect the total noise level. Shielding the exposed areas with acoustic barriers will reduce noise levels. Generally, any part of the engine or drivetrain that can be seen while standing away from the truck will contribute to the total vehicle noise level.
4 – Tires
Many times this is the major noise source for highway trucks traveling at high speeds. The condition of the tires and the tread pattern affect the noise level. At low speeds, this is not a large noise source.
5 – Exhaust System
Worn or inadequate exhaust systems are the largest and the most frequent contributor to high noise levels. A visual inspection and repair of leaking connections or replacement of failed components will noticeably reduce noise levels. If the noise level is still too high, the addition of resonators, packed stacks or a change in mufflers is recommended.
Objectives Of This Manual
Most of us have a good idea of how the exhaust system works and why. Even so, you may not realize that incompatible or inferior exhaust system parts can shorten component life, interfere with proper vehicle function and may even cause serious damage. High quality replacement parts are critical and in the pages ahead you’ll learn why.
In this guide, you will also:
• Master a basic understanding of the heavy and medium duty exhaust system.
• Learn how specific exhaust components and related parts affect overall vehicle performance and fuel efficiency.
• Refresh your basic knowledge about EPA regulations related to exhaust noise.
• Review the Nelson Global Products line of exhaust system products and related items.
How The Exhaust System Works
The primary purpose of the exhaust system is to expel burned gases—or exhaust—to the rear of the vehicle and to dampen the sound of engine combustion.
Exhaust System Components
The major parts of a diesel truck exhaust system include:
• Manifold pipe and connector
• Exhaust pipes and elbows
• Stack pipe or tail spout
Let’s review the primary components of the exhaust system—and how they work together to expel exhaust, reduce noise and assist in smoother running operation.
Although the manifold is often thought to be a part of the engine, it is a key component of the exhaust system. The exhaust manifold is the component, usually made of cast iron, that gathers all the exhaust as it comes out of the head into a single collector. The manifold then delivers the burned gases into exhaust pipes.
The primary purpose of the exhaust pipes is to serve as an enclosed route for the burned gases to exit the system. While exhaust pipes are joined to the manifold by a manifold pipe/connector, there are a variety of ways to assemble the “route” or system.
For example, a vertical dual exhaust system would utilize a manifold pipe with a splitter tee adapter to route the exhaust in two different directions. On the other hand, a Wye Connector would be used in a V-type engine application, typically a medium duty truck. There are also mufflers which feature two inlets — one for each half of a V-type engine — leading to one outlet.
Exhaust Pipe and Elbows
Exhaust pipes and elbows have several important purposes. Exhaust gas is toxic, and these exhaust pipes serve to contain the exhaust and route it towards the rear of the vehicle as quickly and efficiently as possible. The pipes and elbows are used to create an effectively sealed pathway to guide the exhaust gas safely from the engine to the exterior of the tractor/trailer. Exhaust pipes are manufactured in a wide variety of shapes and sizes, although there are basically two types:
• Regular pipe
• Flexible pipe
Regular exhaust pipe is solid, typically available in straight lengths, bent configurations and elbows. Certain applications also require flexibility because the connection must be sealed tightly. At the same time, the exhaust system must be flexible enough to bend with road conditions and accommodate thermal expansion of the system; otherwise the pipe or a connection may snap or break. That is why flexible exhaust pipe is commonly used in larger diesel exhaust systems, heavy duty applications and severe service vehicles. The exhaust system may be sealed by welding joints. Alternatively, instead of welding, exhaust clamps can be used in place of welding as a simple, effective way to seal overlapping pipes.
Aside from school bus applications, which include some extremely strict requirements and regulations, the method for sealing the system is a personal preference of the owner or fleet manager. There are also applications where resonator(s) are used to begin to dampen the noise before it reaches the muffler.
The muffler is the primary component within the exhaust system that reduces the noise made by the engine during combustion; as sound waves enter the muffler chamber, they are broken up and the noise dissipates.
Some types of mufflers include chambers with holes, while others are padded with fiberglass or plates to dampen noise levels. The technical challenge is to use a method that most effectively breaks up sound waves without producing excessive back pressure. Some mufflers start with a more efficient design than others, use heavier gauge materials and rely on better manufacturing processes—and these all make a noticeable difference in quality, maintenance costs and vehicle performance.
The Importance Of Correct Back Pressure
Exhaust gases are passed through the muffler to reduce the noise of engine combustion. At the same time, back pressure causes exhaust gases to remain in the engine cylinder after the exhaust stroke. While a certain amount of back pressure is vital to optimum performance, too much back pressure can result in loss of horsepower and excessive engine/ turbocharger operating temperatures. When this happens, performance and fuel economy suffer. It may not take much to
alter the balance or to affect engine operation.
Always replace components in the exhaust system with like components. When the vehicle was designed, product engineers selected specific exhaust system components and parts to achieve a high performance balance, including the proper amount of back pressure. Replacing an exhaust system part with a like component assures the most efficient performance.
How To Replace The System
When you consider replacing a muffler, that’s the time to think about replacement pipe, new clamps or other related items. If a new muffler or pipe is installed and there is still an exhaust leak, the problem is not fixed.
The best way to select a muffler is to use the OE part number cross reference. If the OE number is not available, use a “Muffler Application By Engine” reference. Many mufflers have the same exterior size but vastly different interior construction and performance.
There are several other items you need to consider before any exhaust system installation or repair.
• Use new clamps anytime a muffler or pipe is replaced. This is also a good time to double-check all other clamps and joints within the exhaust system.
• Thoroughly review the system for special needs, such as rain caps (for a straight stack pipe) to prolong the life of the system. Make sure an existing rain cap is still in place and in good condition.
• On a vertical system, check to ensure that the heat guard around the muffler is in place and secure. If there is no heat shield—you may want to consider adding one.
• Check the system for other components that may need to be replaced.
• Examine the flex pipe (if it is used) to make sure it’s in good condition and will perform properly.
• Starting at the front, do a leak check all the way back. The manifold pipe/connector needs to be checked every time any work is done on the exhaust system.
• Once the system is assembled, it should be checked for leaks after new clamps are put into place and/or welding is complete.
Welding Aluminized Steel
Oxyacetylene Welding Filler Metal
Use a mild steel filler metal, 3/32″ (2.38 mm) diameter, free of rust (American Welding Society classification A5.2). Do not use copper coated filler material.
Use a number 3 or 4 tip. Observe instructions of the equipment manufacturer when adjusting the operating pressures at the gas regulators.
Clean the parts to be welded thoroughly. Incline the torch at a 45° angle from the direction of travel. Use the forehand welding technique. Keep the torch flame on the tip of the filler rod, not in the center of the puddle.
Shielded Metal-Arc (Stick Electrode)
Any one of the following rods are recommended:
• Low hydrogen: E7018
• Stainless: 309 or 310
Gas Metal-Arc (MIG)
• Wire: ER70S-3 or ER70S-6
• Shield gas: Carbon Dioxide or 75% Argon 25%
Top Quality Construction
Heavy duty, medium duty, and most recently, light duty exhaust products are manufactured by Nelson Global Products, the largest OEM supplier of exhaust systems and a leader in engine exhaust noise technology. You can count on Nelson Global Products exhaust system products for OE quality along with consistent:
• Quiet operation
• Low back pressure
• Fuel efficiency
As the global leader in the design of exhaust systems that maximize performance and minimize environmental impact, Nelson Global Products provides the industry’s highest quality products under its Nelson Global Products brand. Nelson Global Products exhaust systems are designed for durability and custom tuned to meet current noise level regulations. The Nelson Global Products product line includes mufflers, non-chrome tubes, stacks and elbows—all premium components constructed of top-grade steel. The steel is aluminized, which means it is treated to resist the corrosive action generated by heavy duty exhaust
systems, even in high temperature conditions.
There are numerous design features that make Nelson Global Products mufflers top rate. Perhaps the most important is the floating baffle design, patented by Nelson Global Products, that relies on a series of small partitions (or baffles) to impede sound waves for maximum noise reduction with optimal back pressure. The perforated tubes and resonator chambers on the inside of the muffler keep noise levels down without restricting the flow of exhaust gas.
Nelson Global Products mufflers are constructed of heavy gauge aluminized steel to:
• Resist hot, corrosive exhaust gases
• Deter rust
• Extend service life
Many of the small diameter horizontal mufflers also feature a heavy duty crimp construction on both ends. This unique feature, approved by OEMs, makes a high-strength, backfire-proof and rust-free seal. Vertical mufflers have special edge welding to provide a strong joint that is also appealing in appearance. Besides this smooth edge, the muffler has a domed head which, on vertical application, prevents moisture from collecting at the top of the muffler.
Nelson Global Products also offers an economy muffler that goes head-to-head with the competition, featuring heavier gauge flanges as well as internal flanges for support. The illustration on the following page shows the difference between Nelson Global Products OE and Nelson Global Products economy mufflers.
Whether you need the full-feature performance of an OE replacement or you’re looking for a lower cost solution, the best choice is Nelson Global Products.
The Nelson Global Products Difference
Why are Nelson Global Products mufflers so much better than will-fit mufflers? Why should you buy a Nelson Global Products OEM approved muffler instead of an aftermarket non-certified copy? The answer starts with the steel. The average exhaust system temperatures of gas and diesel applications range from 800 °F (427° C) to 1400 °F (760 °C).
Aluminized steel holds its strength characteristics up to 1300 °F (705 °C). Nelson Global Products aluminized steel also resists oxidation much longer than unprotected mild steel. Unprotected mild steel used by many will-fit companies begins to rust as soon as it is exposed to everyday field conditions, regardless of its thickness. This mild steel also loses its strength after exposure to minimum exhaust temperatures.
Galvanized steel begins to give off extremely toxic fumes at the minimum 800 °F (427 °C), and immediately loses its rust resistant characteristics.
The superiority of aluminized steel is why Nelson Global Products uses all aluminized steel construction for its exhaust mufflers, non-chrome tubes, stacks and elbows.
When it comes to exhaust systems, there are two basic configurations—vertical and horizontal. If you compare actual components in the sketches of these two systems, you’ll see that there is little variation in parts.
With today’s vertical application, the muffler is bolted to a mast structure. In the past, mufflers were bolted to the back of the cab or tractor; however, this resulted in a great deal of noise transfer. That’s why the majority of trucks now use a mast structure with separate supports off the frame for mounting.
This schematic shows the “plumbing”– or all of the components and exhaust system parts needed for a vertical application. Although this shows a dual exhaust configuration, this kind of exhaust system can also be installed as a single exhaust configuration. You may prefer this vertical stack system as a way to get any objectionable exhaust odor away from ground level. However, there is no regulation or technical requirement for one configuration over the other; this choice is simply a matter of personal preference.
In recent years, the industry has begun to focus more on aerodynamics, so it has become more popular to use a horizontal exhaust system. Mufflers and stack pipes that stick up (as in a vertical application) cause parasitic drag and can detract from fuel mileage. So, in some cases, the choice is made to put the exhaust system underneath the tractor trailer. Again, this is strictly a personal preference.
In some cases, there simply may not be enough room between a tractor and the box in a straight truck to install a vertical exhaust system. At these times, a horizontal configuration is the ideal solution.
What’s important to remember is that it is possible to find a vertical and a horizontal application in any truck class. One configuration may better suit a particular truck due to space constraints, but in many cases, this is a choice based on past experience and/or an individual preference.
School Bus Applications
School bus applications are an exception to the matter of personal preference. In fact, there are some very stringent local regulations for school bus exhaust systems, possibly including requirements for:
• A horizontal application
• Rear exit
• A totally leak free system
Nelson Global Products offers the most complete product coverage in the bus aftermarket with the flexibility to meet your most rigorous requirements, including the high quality assurance and long life vital to this specialized market.
Off-Road Exhaust Systems and Special Mufflers
We also offer a series of mufflers and accessories for off-highway equipment tailoring OEMs. Please see our Exhaust Systems Catalog (NPG005) for details.
How to Troubleshoot the Exhaust System
The following are guidelines to help you locate and identify problem areas in the vehicle’s exhaust system.
• Mufflers. Inspect the area around clamps for breakage, cracks and rust-through. In addition to excess noise, a leak in the muffler can cause cleanup expenses when soot escapes and discolors the cab or trailer. Most importantly, a leaking muffler may allow exhaust gases to escape to the driver compartment causing
sleepiness and even death through carbon monoxide poisoning.
• Elbows, Stacks and Exhaust Pipes. Dents or crushed portions of any tubing create exhaust flow restriction and increase back pressure significantly. Even relatively small dents will cause decreased fuel economy and increased turbo wear. If dents are relatively large, increased bearing and lower cylinder wear will occur due to increased exhaust temperature. In such cases, significant decreases in fuel economy will result.
• Rain Caps. Although Nelson Global Products mufflers are designed to prevent rain, melted snow and sleet from passing beyond the muffler to the engine, rain caps are recommended. Water entering the muffler will create a slurry of soot to be blown on the trailer causing significant cleanup expense. A curved exhaust
stack is an acceptable alternative to a rain cap but may not be 100% effective in hard rains.
• Clamps. Check band clamps for cracking periodically. Reuse of any clamps is not recommended.
• Flexible Tubing. Do not patch. Replace entire section. Stainless steel is recommended as the best value.
• Mounting. The exhaust system should be secured to eliminate vibration. The muffler brackets should fit securely to the muffler and to the mast or truck frame. The muffler brackets should not squeeze the muffler body and the mast must not vibrate or wiggle.
Exhaust System Products Warranty
Perhaps the most commonly replaced exhaust system component is the muffler. In fact, industry data indicate that heavy duty mufflers are replaced every three to four years, while medium duty truck mufflers in certain vocational applications may be replaced as often as every two years. The Nelson Global Products muffler warranty is the best in the industry. Please contact us for warranty details. Chrome plated exhaust system products are warranted, as well, against peeling and blistering within the twelve month warranty period, beginning on final sale date to the end-user owner. Note: This warranty does not cover exhaust system
parts that rust out or are blown out by backfire or other faulty conditions nor exhaust system products damaged or destroyed resulting from incorrect installation, application or operation.
Let’s review the extensive line of Nelson Global Products exhaust accessories and related items.
There are curved and straight stack pipes in popular lengths, available in mirror quality chrome plated (part number suffix “C”) and aluminized steel (part number suffix “A”). People who are serious about the appearance of their truck generally buy chrome stacks, while aluminized stacks are functional and will hold up for the longer haul.
Keep in mind that while many of the competitive alternatives are cheaper, they are often of extremely poor quality. The chrome finishes on these inferior products tend to rust or peel in a relatively short time due to poor manufacturing processes. Mild steel stacks and elbows may be less costly to buy, but because of short service life, they cost more per mile than aluminized steel products.
Nelson Global Products uses an excellent nickel plated, chrome finishing process—and that guarantees the highest quality. Sure, you can buy cheaper alternatives, and they may look good for a short period of time. Simply remind yourself that if you invest a little more in good quality, it is far more cost effective in the long run.
Anytime a muffler or exhaust pipe is replaced, the related clamps should always be changed. Heavy duty clamps are designed for fast, easy and accurate installation, as well as maximum clamping force without crushing pipes. Some of the most widely used options include:
Wide Band Clamp
This type of clamp minimizes exhaust system leaks and holes, protecting the driver in the cab from odorless, poisonous gases which can seep in from the system. This clamp reduces the need for welding the pipe and makes a tight seal without damaging the pipe diameter. It also works for butt and lap installations using either solid-to-solid tubing or flex-to-solid tubing.
This clamp is the most common fastening device on pipes of 2″ (50.8 mm) to 6″ (152.4 mm) diameters.
This type of clamp connects the manifold or turbocharger to the exhaust system and is available to cover the majority of engine applications and sizes.
Flat Band Clamp
This type of clamp is available in either zinc or chrome plated in 3″ (76.2 mm) to 6″ (152.4 mm) pipe diameters.
If you have straight stacks, Nelson Global Products offers a selection of aluminized steel or chrome rain caps, all featuring single bolt mounting and heavy
duty welded assembly for long life. Nelson Global Products rain caps are also precision balanced to keep the rain out, protect the muffler and exhaust system from rust and get rid of carbon residue for good.
Heat Guards and Grab Handles
Nelson Global Products heat guards are available in both aluminized steel and bright stainless steel with various degrees of wrap and hole patterns— all engineered to protect the driver and others from a hot muffler. Nelson Global Products can even personalize heat shields and mufflers with a custom punched pattern, name or logo right into the steel.
Like many of its competitors, Nelson Global Products offers galvanized flex for those who need a product at a very low price. Nelson Global Products also offers stainless steel flex for first class, long life application. Because of the high price of stainless steel, the company now offers a long life aluminized steel flex. This aluminized tubing provides a quality option with affordable pricing, much closer to that of the galvanized tubing than to stainless steel flex hose.
Characteristics Of Nelson Global Products Flex Galvanized flex hose will withstand up to approximately 600 °F (316 °C) before heat breakdown of the coating starts. At this point, the material begins to degrade and rust begins to form.
On the other hand, aluminized coating will withstand conditions over 1200 °F (649 °C) before the aluminum coating starts to soften. Of course, stainless steel flex tubing is designed to withstand high temperatures, such as those found in gasoline engine applications. Its only drawback is a tendency to turn different colors when exposed to very high temperatures, a cosmetic change with no effect on performance.
When it comes to measuring flex tubing, there is a certain amount of disagreement. Different people measure it in different ways; since it’s sold by the foot, disputes can crop up about how much was shipped versus what was ordered. To prevent any misunderstandings, Nelson Global Products recommends a standard method for measuring flex. Since the natural lie of flex is halfway between fully extended and fully compressed, Nelson Global Products flex is currently supplied in fully extended lengths plus 2″ (50.8 mm) extra on 10 foot (3.05 m) lengths, or 6″ (152.4 mm) extra on 25 foot (7.62 m) lengths.
To properly measure flex, coil the tubing in as tight a radius as possible. Now, measure the outside parameter of the coil; this will give the overall, fully extended length of the section of flex. Since flex is generally sold in extended lengths throughout the marketplace, it’s important that accurate measurements be provided by all competitors and distributors. Remember: the extended length is generally 1.2 times the compressed length. This is only an estimate and should not be used as an accurate form of measurement.
There are several ways to cut flex tubing. The method most accepted by the industry is to tack weld the flex on both sides of the cut before actually cutting. With this done, there is no way for the flex to unravel after it is cut. This will also keep the diameter of the flex within tolerances so that it cannot become uncoiled once the part has been cut.
The best and easiest method for cutting flex is plasma cutting, which:
• Leaves a smooth end with no burrs
• Requires little or no trimming
• Does not require hard clamping (which can deform the flex ribs)
The band saw (or hack saw) cutting method is commonly used to cut flex to proper lengths. This method:
• Leaves very rough edges
• Requires the removal of sharp burrs before use
• Requires additional work on the ends to be sure the flex does not grow in diameter
Another method, not often used, relies on a pipe cutter. This type of flex cutting is:
• Not popular or widely accepted
• Needs several different sizes of cutters, depending on the variety of diameters of flex
• Leaves sharp edges which require trimming