If I read things right, motorcycles are exempt from this, as are trucks over 6000gvwr.
Straight from California's auto noise regulation .
27201. For the purposes of Section 27200, the noise limit of 92 dbA shall apply to any motorcycle manufactured before 1970.
(Added by Stats. 1975, Ch. 83.)
27202. For the purposes of Section 27200, the following noise limits shall apply to any motorcycle, other than a motor-driven cycle, manufactured:
(1) After 1969, and before 1973 ........................88 dbA
(2) After 1972, and before 1975 ........................86 dbA
(3) After 1974, and before 1986 ........................83 dbA
(4) After 1985 .................................................80 dbA
27207. No motor vehicle with a gross vehicle weight rating of more than 10,000 pounds and equipped with an engine speed governor shall produce a sound level exceeding 88 dbA, measured on an open site at a distance of 50 feet from the longitudinal centerline of the vehicle, when its engine is accelerated from idle with wide open throttle to governed speed with the vehicle stationary, transmission in neutral, and clutch, if any, engaged. Test procedures for compliance with this section shall be established by the department, taking into consideration the procedures of the United States Department of Transportation.
27204.the purposes of Section 27200, the following noise limits shall apply to any motor vehicle within the specified manufacturer’s gross vehicle weight rating and date of manufacture:
GVWR—Pounds Date of Manufacture Noise Limit—dbA
Over 6,000 after 1967 and before 1973 88
Over 6,000 after 1972 and before 1975 86
Over 6,000 after 1974 and before 1978 83
Over 8,500 after 1977 and before 1982 83
Over 6,000 but not over 8,500 after 1977 80
Over 8,500 but not over 10,000 after 1981 80
Over 10,000 after 1981 and before 1988 83
Over 10,000 after 1987 80