The California Air Resources Board (ARB) regulates aftermarket parts and has promulgated regulations that essentially place all emissions related aftermarket parts into three categories:

(1) Replacement Parts
Replacement Parts are aftermarket parts that ARB considers to be functionally equivalent to the stock part they are intended to replace, and therefore would not impact the emissions from these vehicles. These parts are appropriate for sale and use on motorcycles used on or off the public highways. For aftermarket exhaust systems and parts, there are two applicable scenarios:

(a) If the motorcycle’s stock exhaust system does not contain a catalytic converter, then an aftermarket exhaust part is a replacement part as long as the part does not remove or replace any emission control equipment originally attached to the stock exhaust system, such as oxygen sensors.
(b) If the motorcycle’s stock exhaust system contains a catalytic converter in the manifold section of the stock exhaust system, then an aftermarket muffler positioned downstream from the catalytic converter (i.e. cat-back) is a replacement part as long as the part does not remove or replace any emission control equipment originally attached to the stock exhaust system.

(2) Executive Order Parts
Executive Order Parts are aftermarket parts that ARB has evaluated and determined do not adversely impact emissions, and thereby are granted an Executive Order (EO), which allows the part to be sold and used on specified motorcycles. Any aftermarket exhaust system that replaces or otherwise impacts emission control equipment, including catalytic converters, requires an EO to be sold and used on a motorcycle used on or off a public highway.

(3) Competition Use Only Parts
Competition Use Only Parts may not be sold or used on a motorcycle that is used on or off the public highways other than those motorcycles used exclusively for competition. Competition Use Only Parts are aftermarket parts that replace or otherwise interfere with the operation of an emission control device, such as a catalytic converter or oxygen sensor, and may be sold and used on a motorcycle that is used only for closed course competition.

Harley-Davidson Models with Catalytic Converter:

Touring models 06-Earlier : Located in Muffler [Slip-ons and Headers with out EO# not permitted for use]
Touring models 2008 : Located in Muffler [Slip-ons and Headers with out EO# not permitted for use]
Touring models 2009-up : Located in Headers [Headers with out EO# not permitted for use; Slip-on mufflers are OK]
Softail models 2008-up : Located in Mufflers [Slip-ons and Headers with out EO# not permitted for use]
Dyna models 2008-up : Located in Mufflers [Slip-ons and Headers with out EO# not permitted for use]
Sportster models 2014-up have a Catalytic Converter.
V-Rod models do not have a Catalytic Converter.