Freightliner exhaust guidelines

Freightliner released guidelines to ensure that bodybuilder exhaust modifications to 2007 Business Class M2 trucks are consistent with requirements of the US Environmental Protection Agency (EPA) and the California Air Resources Board (ARB), and also in compliance with engine manufacturers' requirements for exhaust back pressure.

The guide was designed to give bodybuilders more freedom and flexibility in performing exhaust piping modifications downstream of the aftertreatment device (ATD), while staying within the EPA, ARB, and engine manufacturers' requirements.

Vocational product manager Ivan Neblett said EPA ‘07 exhaust systems must be validated as compliant. Any changes to the turbo outlet pipe and/or the ATD could bring the system out of compliance, so changes must be approved by the engine manufacturer and Freightliner LLC to meet US 2007 EPA requirements. Any modifications could significantly alter the performance of the system and invalidate the warranty.

Neblett said the exhaust heat mitigation device effectively reduces the concentration of exhaust gas heat. All exhaust systems with a street-level, horizontal exhaust pipe must use the mitigator. If installed, the mitigator must remain part of the exhaust-piping configuration. Those modifying the vehicle must ensure that the exhaust gas and exhaust system components are located to protect against damage or injury from high temperatures.

Also, those modifying the vehicle must ensure that the final vehicle configuration conforms to all pertinent federal, state, and local requirements, including but not limited to safety, emissions, and noise requirements. Exhaust piping modifications must comply with guidelines and use proper materials. Proper support must be used to adequately support exhaust piping added.

He said that to calculate the pressure loss value for exhaust piping from the ATD exit to the tailpipe exit, go to, then refer to the back pressure equation worksheet (Worksheet A), the component pressure loss value table (Table 1), and the maximum exhaust piping pressure loss value tables (Tables 2a and 2b).

Starting with Worksheet A, fill in the exhaust piping component quantities and multiply by the component pressure loss values (from Table 1) to calculate the component total back pressure. Sum the component totals to get the calculated back pressure for the piping modification. If the calculated value is less than or equal to the maximum value listed in Table 2a or 2b, the exhaust piping should meet engine manufacturer's back pressure requirements.

Neblett said all Freightliner 2007 emission-compliant vehicles require elevated exhaust temperatures to effectively remove collected soot in the diesel particulate filter (DPF). The Freightliner exhaust heat mitigation tailpipe reduces the concentration of exhaust gas heat and is required for all horizontal tailpipe exhaust outlets. The mitigation device has been designed to disperse exhaust gas producing the thermal distribution representative of active regeneration events for a variety of engine operating conditions, including idling speeds.

In the Exhaust Tailpipe Design Guideline, a minimum distance of 150 mm from tailpipe to outer edge of the body is strongly recommended. For exceptional cases where this can't be achieved, the distance should be maximized as much as possible with 50 mm being the minimum allowable distance. Typical exhaust gas temperature distribution zones have been provided for relocation guidance in these cases.

He said he highly recommends that the tailpipe never be relocated from the position installed by the original vehicle manufacturer. Relocation of a horizontal exhaust tailpipe outlet is acceptable but not recommended by Freightliner. Alternative tailpipe designs are available from Freightliner

The exhaust tailpipe is to be installed so that the outlet face is located directly downward. The outlet face should be parallel to the ground within five degrees. Never point the exhaust upwards or towards any vehicle components.

He said vehicle components (tires, hoses, frame rails, etc) should be located no closer than 300 mm from the exhaust tailpipe outlet in the transverse, underside, or exhaust gas flow directions; and 50 mm from the top surface of the exhaust tailpipe. Retain the original ground to tailpipe clearance as installed by the vehicle manufacturer. The tailpipe must be no lower than the bottom of the ATD.

Neblett said the mitigator is made of aluminized 409 stainless steel. Attention should be given to the materials of the connecting pipes for possible galvanic corrosion. Proper weld materials must be used for correct joint creation when using aluminized 409 stainless steel. It is recommended that the tailpipe be secured to another pipe that is connected to the outlet of the ATD using a marmon style, V-band clamp, an exhaust seal clamp, or direct welding.

The 16K AWD multi-leaf spring rear suspension for all-wheel-drive trucks has a data code of 622-1G3 and is used with a 10K front drive axle (400-1D4). The 12K flat-leaf suspension has a data code of 620-002 and provides enhanced front-end stability for boom/crane/manlift trucks. The M2 snow shield has a data code of 701-008 and protects the cab's HVAC air intake. The under-step mounted ATD with vertical tailpipe has a data code of 016-1BU and is designed for dump, tank, and utility bodies.

Neblett said Freightliner also created an additional system that can be ordered straight from the factory: a right-hand under step mounted horizontal ATD with right-hand horizontal tailpipe. It has a data code of 016-1BT, is available on M2106 day/extended/crew/all-wheel-drive vehicles, and is designed for fire/emergency and utility vehicles, and RVs.

Available starting in December with Cummins ISB and ISC is the right-hand under step mounted horizontal ATD with right-hand horizontal tailpipe. It has a data code of 016-1B6, and will replace the 016-1BT.

“It sits above the bottom of the transfer case, so your exhaust pipe should not have any interference as far as ground clearance,” Neblett said.

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