Mr. Tom Dillon

2296 Nichols Road, Apt. F

Arlington Heights, IL 60004

Dear Mr. Dillon:

Thank you for your recent letter in which you requested some information about the requirements for exhaust repair and other modifications to motor vehicles. Enclosed are some fact sheets and letters to various people in the repair industry which explain the type of repairs and modifications that can be performed without being liable for violations of the Federal tampering prohibition. The information confirms that repair shops cannot install dual exhaust systems on vehicles which came from the factory with single exhaust systems.

Federal law prohibits any person from removing or rendering inoperative any device or element of design installed on or in any motor vehicle or motor vehicle engine originally certified to meet federal emissions standards. Exhaust backpressure and the exhaust system configuration are elements of design of the emission control systems as certified by the vehicle manufacturers. Therefore, any changes to those systems could be considered violations of federal law.

Backpressure can affect emissions, and a decrease in backpressure would normally be expected to increase tail-pipe emissions, particularly oxides of nitrogen and hydrocarbons. The addition of a second catalytic converter as part of a dual exhaust system would not necessarily reduce the exhaust emissions output of the vehicle. In fact, reducing the flow to each converter of a dual system could actually extend the time necessary for the converter to light-off (warm up and start operating) thereby causing much higher cold start emissions. Cold start operation is the period during operation when the highest emissions normally occur.

Your options, therefore, appear to be limited to keeping the vehicle in a single exhaust configuration. Although I realize this is not the answer you were probably hoping to receive, the laws and our policy regarding these matters is fairly explicit. If you have any further questions concerning this matter, please feel free to contact me at (202) 233-9003.

Sincerely,

Steve Albrink

Office of Mobile Sources

Enclosures

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