police pulled me over today tried to say my muffler was too loud and defective i told the officer that my car is 25 years old and i am exempt from all muffler emissions and exhaust noise ordinances because of that, officer went to his car for about to minutes and came back he said thank you and handed my liscence registration and insurance back then he left.. i win 
i have a 1986.5 but the 1987 is now also a 25 year old car
http://law.justia.com/codes/washington/2005/title46/46.37.390.html
(3) No person shall modify the exhaust system of a motor vehicle in a manner which will amplify or increase the noise emitted by the engine of such vehicle above that emitted by the muffler originally installed on the vehicle, and it shall be unlawful for any person to operate a motor vehicle not equipped as required by this subsection, or which has been amplified as prohibited by this subsection. A court may dismiss an infraction notice for a violation of this subsection if there is reasonable grounds to believe that the vehicle was not operated in violation of this subsection.
This subsection (3) does not apply to vehicles twenty-five or more years old or to passenger vehicles being operated off the highways in an organized racing or competitive event conducted by a recognized sanctioning body.
i have a 1986.5 but the 1987 is now also a 25 year old car
http://law.justia.com/codes/washington/2005/title46/46.37.390.html
(3) No person shall modify the exhaust system of a motor vehicle in a manner which will amplify or increase the noise emitted by the engine of such vehicle above that emitted by the muffler originally installed on the vehicle, and it shall be unlawful for any person to operate a motor vehicle not equipped as required by this subsection, or which has been amplified as prohibited by this subsection. A court may dismiss an infraction notice for a violation of this subsection if there is reasonable grounds to believe that the vehicle was not operated in violation of this subsection.
This subsection (3) does not apply to vehicles twenty-five or more years old or to passenger vehicles being operated off the highways in an organized racing or competitive event conducted by a recognized sanctioning body.