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Prohibited Exhaust Systems

The following section contains photo examples of loud aftermarket exhaust systems and definitions that are designed to allow police (as well as vehicle owners) to easily identify them. None of these examples of exhaust systems and mufflers meet EPA noise emissions standards.

Aftermarket Muffler

An aftermarket exhaust system that replaces the factory-installed muffler.

Harley-Davidson Screamin’ Eagle brand aftermarket exhaust system for a Harley-Davidson FLT.

Straight-Pipe Exhaust Systems

A motorcycle exhaust system that has the outward appearance of a uniform, consistent diameter for the entire length of the system.

Straight-pipe exhaust systems are aftermarket exhaust systems that no motorcycle manufacturer has ever installed on a production motorcycle directly from the factory. These systems are designed solely to make noise and produce sound levels far in excess (10–20 dBA) of current EPA manufacturing requirements. This is perceived by the human ear as three to five times louder.

It is impossible for any straight-pipe exhaust system to come close to being an effective muffler. These exhaust systems do not have an expansion chamber to disperse sound waves and slow down exhaust gases, nor do they incorporate any sound-dampening material or reverse-flow passages and chambers, as original equipment motorcycle mufflers have for the past forty years. They rely on exhaust restriction principles (when baffles are installed) to reduce noise emissions.

Baffles

A removable aftermarket motorcycle exhaust system component designed to reduce exhaust noise.

Baffles are typically small and very ineffective devices that, when installed in straight-pipe exhaust systems and some hollow-core mufflers, make these exhaust systems legal under most states’ laws. Below are examples of the most common types.

Hollow-Core Muffler

A muffler in which the exhaust inlet is visible from the exhaust outlet.

Open-center or hollow-core mufflers are absorption-type mufflers. They utilize an expansion area and usually sound-dampening material but have an unobstructed internal passage straight through from the muffler inlet to the outlet with very little obstruction. As one might suspect, a muffler that one can see straight through cannot be very effective. These exhaust systems can easily be identified by simple inspection by police and inspection mechanics.

D&D aftermarket exhaust system for a 2003 Kawasaki ZRX1100

Kerker brand aftermarket exhaust system for a 1976 Kawasaki 1000