An exhaust system is usually tubing used to guide waste exhaust gases away from a controlled combustion inside an engine. The entire system conveys burnt gases from the engine and includes one or more exhaust pipes.
Exhaust systems perform four basic functions: direct burned gases away from the engine and passengers, dampen noise, enhance performance and control emissions. On trail bikes, a fifth function is performed: spark arresting. Moving from the engine to the back of the motorcycle, the major parts of the exhaust system are: exhaust cooling flange (handles exhaust immediately from the exhaust valves); exhaust pipe, catalytic converter (on a few bikes to reduce emissions); the muffler (reduces broad band noise); and spark arrestor (incorporated into the muffler design).
The exhaust system is designed according to use. Trail, motocross and dual purpose motorcycles route the exhaust high on the frame to keep the system from being damaged in the brush or submerged in water. Cruisers, and bikes designed for riding two people, will route the exhaust low on the frame to allow for a passenger on the back and to create a lower center of gravity. Sport bikes and racers route the exhaust so to reduce back pressure and maximize engine performance, which may be high, low or somewhere in between.
In the past, mass produced bikes came with dismal exhaust systems. The exhaust was one of the first components to be modified. A simple change of the exhaust system delivered whopping increases in power. This is no longer the case. Modern motorcycles right off the showroom floor come with advanced exhaust systems. It is an old wives' tale that modifying the exhaust system will improve performance on a contemporary motorcycle. Even a straight pipe does not help performance of modern emission controlled bikes. Check with an expert before modifying the exhaust system. Your plans may actually decrease performance or require rejetting of the carburetor. Be particularly conscientious when replacing a two-stroke exhaust system. Two-stroke exhaust systems are designed to assist in the scavenge and intake of the cylinder through the control of secondary reverse exhaust gas pulses. Depending on the overall system design, the exhaust gas may flow through one or more of: