To ensure that exhaust modifications by body builders to 2007 Business Class M2 trucks are consistent with requirements of the US Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) and also in compliance with engine manufacturer's requirements for exhaust back pressure, Freightliner engineers have developed guidelines.
The guide is designed to provide more flexibility in performing exhaust-piping modifications downstream of the aftertreatment device (ATD) while staying within the EPA, CARB, and engine manufacturer's requirements.
Freightliner says that EPA '07 exhaust systems must be validated as compliant. Any changes to the turbo outlet pipe and/or the ATD may bring the system out of compliance. Therefore changes must be approved by the engine manufacturer and Freightliner LLC to meet US '07 EPA requirements. Any modifications may significantly alter the performance of the system and invalidate the warranty.
According to the guide, 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. Body builder and/or persons modifying the vehicle must ensure that the exhaust gas and exhaust system components are located to protect against damage or injury from high temperatures. Body builder and/or persons modifying the vehicle must ensure that the final vehicle configuration conforms to all pertinent federal, state, and local requirements, including safety, emissions, and noise requirements.
The guide offers a caution to use the same size and material to extend or shorten original tailpipe. Any additional extensions and bends will change the internal gas pressure, which could result in damage to the ATD or other engine components as well as a reduction in fuel economy.
All Freightliner '07 emission-compliant vehicles require elevated exhaust temperatures to effectively remove collected soot in the 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 distribution representative of active regeneration events for a variety of engine operating conditions, including idling speeds.
Allowable distance
The guide strongly recommends a minimum distance of 150mm from the tailpipe to the outer edge of the body. For cases where this can't be achieved, the distance should be maximized as much as possible, with 50mm being the minimum allowable distance. Typical exhaust gas temperature distribution zones have been provided for relocation guidance in these cases.
The guide also strongly 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 LLC service network that may be more appropriate for specific vehicle applications.
The exhaust tailpipe is to be installed such that the outlet face is located directly downward. The outlet face should be parallel to the ground within 5 degrees. The exhaust should never be pointed upwards or towards any vehicle components.
Vehicle components (tires, hoses, frame rails, etc) should be located no closer than 300mm from the exhaust tailpipe outlet in the transverse, underside, or exhaust gas flow directions; or 50mm from the top surface of the exhaust tailpipe. The original ground-to-tailpipe clearance as installed by the vehicle manufacturer should be maintained. The tailpipe must be no lower than the bottom of the ATD.
The mitigator is made of aluminized 409 stainless steel. The guide says that 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.