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On-Highway Exhaust Product Solutions:

There are a number of materials used in heavy duty exhaust applications. Some of the materials are appropriate for heavy duty applications. Other choices are not durable at the temperatures generated by gas and diesel engines and should be avoided if acceptable service life is desired. Material selected must not only survive high temperatures, but also serve vibration, corrosive exhaust gasses, and external corroding agents such as salt and water.

The materials generally considered for exhaust parts are as follows:

  • Low Carbon Cold Rolled Steel (CRS)
  • Aluminized Steel
  • 300 Series Stainless Steel
  • 400 Series Aluminized Stainless Steel
  • 400 Series Stainless Steel
  • Galvanized Steel

COLD ROLLED STEEL (CRS) is a very poor choice for any exhaust system part. This material is extremely susceptible to corrosion.

These parts are only used when the lowest possible cost is desired. It is rare to find mufflers made out of (CRS), but there are stacks offered in some markets in (CRS). Clamps are another product commonly produced out of (CRS). Clamps are not exposed to the corrosive acids found in exhaust gasses but the high temperatures cause clamps to degrade rapidly in appearance and function. (CRS) clamps can be very difficult to remove after a short time in the field.

ALUMINIZED STEEL is the preferred material for most heavy duty applications. Aluminized steel is a low carbon steel with a thin layer of aluminum alloyed to the surface. The aluminum provides galvanic protection for the base material. Aluminized Steel parts have an ultimate service temperature of 1250° F with a  continuous duty temperature of 1100° F. This material has excellent corrosion resistance to acidic diesel exhaust gasses. Aluminized Steel parts provide excellent field life at a reasonable cost.

300 SERIES STAINLESS STEELS are also applied in exhaust systems. The most common material is Type 304. This material has excellent corrosion resistance and very good high temperature strength and is used in some mufflers applications where very high stresses occur. It is also used as a premium material for gas applications. The most prevalent use of this material in diesel heavy duty

applications is for flex pipe. Flex pipe produced from

light gauge 304 Stainless Steel is an excellent choice

considering all the factors of cost, durability, and service life. In general field service life with stainless steel flex pipe is very good if the flex tubing is installed properly.

400 SERIES STAINLESS STEEL are used for extended service life in diesel applications, and often in gas applications due to their higher operating temperatures. This material family provides slightly better strength at exhaust system temperatures than aluminized steel. The most common 409 Stainless Steel is stronger than aluminized but has cosmetic problems at exhaust system temperature. At first exposure to high temperature it discolors, and over time it develops a nondestructive coating of surface rust. After an extended time in the field a 409 product generally will display external discoloration and look worse than a similar aluminized part. Parts made with type 409 generally require some type of paint or other coating to slightly delay the onset of external discoloration, and the parts will hold a magnet due to higher iron content. Another choice is 409 Stainless Steel with an aluminized coating. Aluminum 409 is used on Diesel Catalytic Converter mufflers due to its excellent high temperature resistance and the corrosion protection of the aluminized coating. This is a premium material found primarily on emission products or high temperature gas applications.

GALVANIZED STEEL parts are sometimes used in the exhaust market. Galvanized Steel has very poor field performance. This material has an upper temperature limit of approximately 600° F. At temperatures greater than 600° F the material rapidly corrodes with a resulting degradation in appearance and probable failure. Galvanized Steel is often used in flex pipe as a low cost replacement part. The initial low cost is offset by the limited field life of the product.

CHROME PLATED COLD ROLLED STEEL (CSR) parts are often found on exhaust systems. This material is a reasonable choice when a bright mirror finish is desired. Corrosion from the inside of the product can still occur. Chrome parts are very challenging to produce. It is important to produce the parts with a high level of quality because surface irregularities (and field damage to the surface) will lead to external rust.
An alternate choice for chrome parts is Bright Annealed Stainless Steel. This material provides a bright mirror like finish with excellent exhaust life service life. The material is costly, but part of the cost increase is offset by using lighter gauges.

1. Make sure your muffler is recommended by the muffler manufacturer for the particular engine in your vehicle. To meet the new noise laws, the “universal” must be replaced by a muffler designed specifically for the engine.

2. Tail pipes on horizontal exhaust systems should be tipped toward the center of the vehicle to avoid noise reflection off the road.

3. If you have curved stacks, replace them with straight stacks. Noise from a pipe outlet is directional and straight stacks will throw noise up, not to the side.
Rain stacks and 45° cut stacks do not appreciably affect noise levels.

4. The length of stack installed on the muffler can be critical. If an irritating “rap” is heard at certain engine speeds, try stacks with different lengths.

5. In an exhaust system with piping exceeding 10 feet in length, the muffler is suggested to be installed where the exhaust pipe to the muffler is either one–half or four times the length of the tail pipe.

6. A resonator can be used in–line with the recommended muffler for additional noise reduction.

7. If you have increased the size of the exhaust piping or made a dual out of a single system, check recommendations for piping size. Over–sized systems are exceedingly noisy!

8. The vehicle operator, to a certain extent can control his vehicle noise. The greater the engines load the louder the noise. Certain engine speeds may be noisier than others. High vehicle speed causes more tire noise. Operating an engine brake when it’s not needed may cause extra noise.

9. If the above mentioned techniques do not solve your problem, contact Nelson Global Products technical support for recommendations.


In an exhaust system, attenuation refers to the reduction in sound level measured between an engine without a muffler and the same engine with a muffler. This sound level is typically measured in a decibel scale (dBAs). See chart below for examples:
Familiar Sounds on the dBA Noise Scale


Backpressure is the force necessary to flow exhaust gas through the system. Backpressure reduces horsepower and fuel economy – for turbocharged diesel engines – about 0.5% decrease in horsepower and fuel economy per inch Hg backpressure.

Typically measured in inches of mercury (Hg) or inches of water H2O) – 1.0” HG – 13.6” H2O.

Cubic feet per minute of airflow.

The sound level measured in decibels using a sound level meter weighted for the “A” scale frequency response. It has over 82% correlation with loudness as determined by the typical human ear (dB without the “A” scales weighting overall has only 70% correlation to loudness).

A unit used to express the relative difference in acoustic power. Whenever dB is used a reference level is implied. The reference value of 0.0002 dynes/cm2 = 0dB.

Diesel Oxidation Catalyst (DOC) Muffler. This muffler design contains a catalyst inside that reduces emissions while reducing exhaust noise. Also referred to as a catalytic converter muffler (CCM).

Diesel Particulate Filter (DPF) Muffler. This muffler design contains a particulate filter that requires Ultra Low Sulfur Diesel fuel. The filter eliminates a greater amount of particulate matter compared to a DOC Muffler, but has a higher activation temperature (260°C. Like a DOC it also reduced emissions while reducing exhaust noise.

A test that allows an engine to be run to full horsepower and raised RPM while remaining stationary.

The sound level of the exhaust system, typically measured in dBA.

Naturally aspirated

A device inserted in the exhaust system ahead of the muffler that provides additional exhaust noise silencing without adding significant backpressure.

sound level measuring device that includes a microphone, an amplifier, an output meter and sound frequency networks for measuring sound levels in decibels.

The sum of exhaust noise level measurement plus fan, intake, mechanical and tire noise. Noise levels add logarithmically (equal noise levels combined add 3 dB; example 75 dB + 75dB = 78 db.


Flexible tubing can twist or unravel when cut, causing its diameter to change and make installation difficult. This occurs because flexible tubing must maintain flexibility in order to function properly, and therefore, cannot be tightly wound in the manufacturing process. However, flexible tubing can be managed for trouble–free installation by following these guidelines.

Step 1: Prepare
Place a tack weld between convolutions each side of on each side of the intended cut to keep ends from twisting or unraveling. If a welder is not available, insert a mandrel or back–up pipe into the tubing and place a punch mark directly on convolutions on each side of the intended cut. Heavy – duty tape over a de–reased pair also works. Cut through tape and leave in place, clamp over tape.

Step 2: Cut
Place the tubing securely in a vice. Cut with a metal cutting band saw or a hacksaw with 32 teeth per inch.

Step 3 – Trim
Each side of the cut will now leave a spiral “tail” that must be removed to the point at which it is attached. Bend each tail until it breaks, or bend and use a cutting
shear to remove.

Step 4 – Deburr
Deburr both cut surfaces with a hand–operated drum sander or file.


Flexible tubing’s function is to prevent excessive stress on exhaust system components by absorbing vibration and thermal expansion that would otherwise cause system components to shake loose and break.

To provide adequate flexibility, flex tubing should be installed in a half extended state. To reach half extension, place the middle of the tubing over the edge of
a work bench, push down on both halves and bend as much as possible.

Then place the entire piece of tubing on the work bench and push down until straightened. The tubing is now at half extension.

Do not use flexible tubing to form an exhaust pipe bend. Use elbows instead.


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