Performance
An aftermarket exhaust can increase performance in two ways. Firstly, it sheds weight. Exhaust makers often use featherweight, ultra-thin metals in their systems. Sometimes, they even “forget” about bulky things like catalytic converters. The result is a slimmed-down system that can save nearly 20 pounds.
The second performance benefit is power; both horsepower and torque can be improved by an aftermarket exhaust. This seems weird at first, because whatever happens in your pipes comes after the engine cycle. But think about it like this: changing your exhaust will change how your engine breathes . If the motorcycle can breathe more air through the engine, and the fuel intake is increased accordingly, you’ll get more combustion. And bigger explosions make more power.
With a full exhaust system and the corresponding fuel adjustment, significant top-end power gains are achievable. In some cases, it can be north of 15%.
Noise
When you play the trumpet (like a boss), the brass amplifies the sound from your lips. When you make the same buzzing sound into a tuba (like a huge boss), the instrument emits a different noise. Same source, different modifiers.
Motorcycle exhausts work in the same way. Your engine makes the sound, and the exhaust modifies it. Since internal combustion is really loud, most exhausts try to muffle the noise. By reflecting pressure waves back on each other, much of the sound is cancelled before it escapes the muffler.
However, exhausts don’t just decrease volume. Depending on the materials, diameters, shapes and interior pores, the sound can be altered in other ways. Whether you ride a 49cc scooter or a 2.3L Rocket III doesn't make much difference. The pitch can be high or low, and the timbre can be full or “tinny.” Exhaust notes can be rough or smooth and, of course, the volume can be loud or quiet. Whatever noise you’re looking for, there will be an exhaust out there to make it.
Of course, there’s no guarantee how a particular exhaust will sound on your particular bike. But YouTube has plenty of hints.
Style
High mount and low mount, shiny and matte, big and small.
There are plenty of flavours to choose from, and the “right choice” is whichever one tickles your fancy. At the end of the day, any aftermarket exhaust is going to set your bike apart from the factory-stock crowd.
One thing to keep in mind: exhausts change color. Thanks to heat cycles and pollutants, almost every system will see discoloration. To slow down - or speed up - this process, see our section on exhaust bluing.