1. (a) Measuring Site. The vehicle under test shall be positioned either on outdoor pavement or on a shop floor (but not over a hoist or pit) in a location where the exhaust outlets are near an open shop door. No sound-reflecting surface other than the pavement and the vehicle being measured shall be within 10 ft (3.0 m) of any part of the vehicle.

2. (b) Microphone Location. The microphone for the sound level meter shall be at the same height as the center of the exhaust outlet. The microphone shall be no closer to the pavement than 8 in. (203 mm) when the exhaust outlet is lower than this height (Figure 1). The microphone shall be positioned with its longitudinal axis parallel to the ground, 20 ± 1 in. (508 ± 24 mm) from the nearest edge of the exhaust outlet, and 45 ± 10 deg from the axis of the outlet (Figure 2). For exhaust outlets located under the vehicle body, the microphone shall be located at the specified angle and at least 8 in. (203 mm) from the nearest part of the vehicle. For exhaust outlets that make an angle of 45 deg or less with the longitudinal axis of the vehicle, the microphone shall be outboard of the exhaust axis. For exhaust outlet angles of more than 45 deg, the microphone shall be on the side of the exhaust axis to the rear of the vehicle (Figure 3).

   

   

   

   

3. (c) Engine Operation. The engine shall be at normal running temperature with the transmission in neutral. Sound level measurements conducted for certification by exhaust system manufacturers shall be made at an average steady-state engine speed of three-quarters of maximum rpm. Sound level measurements conducted by licensed muffler certification stations shall be made at an average steady-state engine speed of 3,000 rpm for vehicles manufactured before 1972 for which the station does not have maximum rpm data.

4. (d) Exhaust Sound Level Measurement. The recorded exhaust system sound level of a stationary vehicle shall be the highest reading obtained during the test, disregarding unrelated peaks due to extraneous ambient noise. When there is more than one exhaust outlet, the reported sound level shall be for the loudest outlet. When there are two or more exhaust outlets separated by less than 12 in. (305 mm), measurements shall be made on the outlet closest to the side or rear of the vehicle (Figure 4). The sound level for motor vehicles with manufacturers' gross vehicle ratings of less than 6,000 lb (2,722 kg), except motorcycles, shall not exceed the following limit:

   1. (1) Sound Level Limit. The exhaust noise shall not exceed 95 dB(A).
   2. (2) Exception. The exhaust noise of vehicles manufactured after 1967 may exceed 95 dB(A) if the replacement parts are no louder than the original equipment or “factory duplicate” system and the total sound level of the vehicle when tested in accordance with Sections 1040 through 1049 of this title complies with the limits in Vehicle Code Section 27205 for the year of manufacture of that vehicle.

Exhaust systems for motor vehicles, other than motorcycles, with a manufacturer's gross vehicle weight rating of less than 6,000 lb (2,722 kg) shall comply with the specified noise limits when tested in accordance with the following specifications: