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Aftermarket Exhaust Product Guide:

Nelson Global Products designs, manufactures and markets high performance OEM and aftermarket products for the global commercial vehicle, on-highway and off-highway markets. Our engineering is the best in the industry and employs the latest design and manufacturing techniques. We are the largest OEM supplier of exhaust systems and a leader in engine exhaust noise technology. Customers can count on our exhaust system products for OE quality.

Top Quality Construction
Our mufflers are constructed of heavy gauge aluminized and stainless steel to:
• Resist hot and corrosive exhaust gases
• Deter rust
• Extend service life

Note: Aluminized steel tubes are not recommended for 2007 emission compliant engines. As the industry leader, we have the ability to manufacture stainless steel tubes and other accessories to meet the stringent 2007 emission regulations. Please call (608) 719-1800 to speak to an OEM account manager for details.

Objectives of This Guide

• Provide a basic understanding of the exhaust system to assist in identifying replacement part needs

• Provide an understanding of how exhaust components effect overall vehicle performance and
fuel efficiency

Troubleshooting and Repairing the Exhaust System
The following guidelines are intended to help locate and identify problem areas in the vehicle’s exhaust system:

Entire Exhaust System – Check the system for leaks from the manifold pipe connector before and after repairs are made.

Mufflers – Inspect the area around clamps for breakage, cracks and rust-through. A leaking muffler represents a potential safety hazard as it may allow exhaust gases to be discharged near, or under, the operator’s compartment creating the potential for carbon monoxide to enter the compartment. Carbon monoxide is a colorless, odorless, but toxic gas. On vertical systems, check to ensure that the heat guard around the muffler is secure and in place. If there is no heat shield you may want to consider adding one.

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. Always check for dented pipes and do not over-torque clamps as this can lead to pipe crimping.

Rain Caps – Our mufflers are designed to prevent water and snow from passing beyond the muffler to the engine. Water entering the muffler will create a slurry of soot and be blown on the trailer later causing significant cleanup expense. A curved exhaust stack is an acceptable alternative to a rain cap but may not be 100 percent effective in all conditions. Make sure an existing rain cap is in place and still in good condition.

Clamps – New clamps should be installed anytime a muffler or pipe is replaced. Check the general condition of all clamps and joints in the exhaust system. Reuse of any clamps is not recommended.

Flexible Tubing – Do not patch flexible hose (flex), always replace the entire section. Stainless steel flex is recommended as the best value due to its superior high temperature strength and oxidation resistance as compared to other materials. Examine any flex pipe to make sure it’s in good condition and will perform properly.

Mounting – The exhaust system must be secured to eliminate vibration. The muffler brackets should fit securely to the muffler and to the mast or truck frame.

How to Reduce Exhaust-Related Noise Levels

1. Worn or leaking flexible tubing is a common noise source. Replace the part, if necessary. The service life of flexible tubing can be improved if it is installed in a relaxed position. Bending, stretching and compressing all reduce life because they limit the tubing’s ability to “flex.”

2. The entire exhaust system should be well-supported. This will reduce the noise generated by the exhaust pipes and

the muffler shell. Care must be taken to isolate engine vibration from the exhaust system and to provide for expansion when the system is hot.

3. The addition of a universal resonator, silenced “wye” or splitter muffler in the system will generally reduce the exhaust noise level from 3 to 6 dBA. Packed stacks will reduce the noise level 3 to 4 dBA. Both items have a minimal effect on engine backpressure.

4. Change from a single to a dual system. For maximum benefit, special “dual only” mufflers are usually recommended. Lower system backpressure is generally an additional benefit of dual systems.

5. On horizontal systems, the tail spouts should be pointed towards the center of the roadway. This reduces the noise reflected off of the road surface and perceived by curbside observers.

6. On vertical systems, straight stacks will yield lower sound levels than will curved stacks. Straight stacks direct the noise upward, where curved stacks direct noise towards the observer.


There are two basic exhaust system configurations – vertical and horizontal. Comparison of the illustrations of these two systems shows there is little difference in the components used. In most vertical installations the muffler is bolted to a mast structure in order to reduce the amount of muffler noise transferred into the cab or tractor. Vertical stacks help to get any objectionable odor up in the air – away from ground level. Vertical installations are also perceived as being quieter because sound is directed upward by the stacks. The need for improved aerodynamics has led to the increased usage of horizontal exhaust systems. The schematics show the overall layout of the components used in both vertical and horizontal installations. It is possible to find a vertical and a horizontal application in any truck class.

School bus applications must meet some very stringent local regulations for school bus exhaust systems that may include a horizontal system, a rear discharge, and a totally leak free system.

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