Improvements

• Aftermarket exhausts can actually improve your car's performance because subtle size or shape differences in the pipes can permit a quicker, more efficient path for the exhaust gases to escape. According to the Auto Media website, some manufacturers claim that their aftermarket exhaust systems can boost your engine's performance by 40 horsepower.
  
  Because most aftermarket exhaust pipes are wider than stock pipes, they can make your car sound louder and deeper, or more "growly," than stock exhaust pipes.
  
  

Features

• Generally, there are two types of bends in exhaust pipes. A crush bend creates a crinkled area on the inside of the bend, which decreases the pipe's diameter and slows exhaust gas. A mandrel bend has a smooth, constant diameter, which provides less resistance to the gases and is therefore more efficient, increasing performance.
  
  In addition to possibly having a different shape, most aftermarket exhaust pipes have larger tips with highly polished mufflers for an enhanced look.
  
  Most factory exhaust pipes are made of mild steel, which deteriorates over time. When you're shopping for aftermarket exhaust pipes, look for aluminized steel or even stainless steel for maximum longevity. Stainless steel pipes expand noticeably when they're hot; after some time, the exhaust joints can work themselves loose so that they rattle when they're cold.
  
  

Choosing

• When choosing an exhaust system for your car, keep in mind all the features you want and your budget. As exhaust pipe diameter increases, performance also increases, but if you get a diameter that is too big for your car, you could damage the pipe and your car. For optimum fitting, try to buy a system that's been designed to work with your car make, model and year.
  
  You can buy a used aftermarket exhaust system, but make sure it can pass inspection. Since 1992, exhausts have been required to help clean up engine emissions before venting them into the atmosphere.