i ran a search, but i didnt see anything with this in it. mods, i apologize if this is somewhat of a duplicate topic. please lock as needed
this is from the vehicle regulation book (2006) for california.

Modification of Exhaust Systems

27151. (a) No person shall modify the exhaust system of a motor vehicle in a manner which will amplify or increase the noise emitted by the motor of the vehicle so that the vehicle is not in compliance with the provisions of Section 27150 or exceeds the noise limits established for the type of vehicle in Article 2.5 (commencing with Section 27200). No person shall operate a motor vehicle with an exhaust system so modified

so we jump to section 27150, which states that you basically need an adaquate muffler...so whatever. everyone knows this. now lets go to to the second part of the OR which i italicized. 27200 really deals with dealers selling vehicles that have modified exhaust...but attatched to section 27200 is section 38270

Noise Limits

38370. (a) The Department of Motor Vehicles shall not identify any new off-highway motor vehicle, which is subject to identification and which produces a maximum noise level that exceeds the following noise limit, at a distance of 50 feet from the centerline of travel, under test procedures established by the Department of the California Highway Patrol.

(1)Any such vehicle manufactured before January 1, 1973 - 92 dBA

(2)Any such vehicle manufactured on or after January 1, 1973, and before January 1, 1975 - 88 dBA

(3)Any such vehicle manufactured on or after January 1, 1975, and before January 1, 1986 - 86 dBA

(4) Any such vehicle manufactured on or after January 1, 1986 - 82 dBA

looks like an 82 dBA limit. now to my question...it states something about CHP having test procedures. can you:
1) go directly to CHP, have your dBA level tested and approved by CHP. and get a legal signed copy of it so cops dont bother you about it?

and

2)has anyone conducted a dBA test for their exhaust system to see if it meets the requirements for your state? any results?

 

Actually, you missed 27151 (b) Even though I can't find published information of SAE J1169 May 1998, I believe the testing procedure is to measure 20 inches from the exhaust exit at nominal operating RPM, which in our case would be 2500-3500 RPM. The only place you can receive an approved measurement is at specific referee stations.

 

ah i see u beat me to it 2fast...good find for him