The aftermarket auto parts industry is what is referred to as a secondary market. This secondary market is filled with alternative, extra and sometimes used performance auto parts that do not come with a vehicle in "stock", also known as factory condition. Aftermarket performance parts are installed vehicle parts, chemicals, equipment and tools or other accessories which are available after the original sale of the vehicle by the original equipment manufacturer (OEM) company.The aftermarket valve plate manufacturers and accessories business does upwards of $250 billion in the United States alone. These types of products cover replacement parts (due to age or accidents) and tweaks to performance, appearance or tuning, even electric and alternative fuel conversion. However the bulk of the aftermarket performance auto parts industry is indeed for tuning and often full-on racing. This industry also employs nearly 5 million people in the United States, via manufacturing companies, distribution companies, retail and repair shops.Turbo KitsTurbochargers, which are different than superchargers or twinchargers, are perhaps the most popular aftermarket performance racing parts. A turbo charger is centrifugal compressor. This compressor receives power from the engines exhaust gases via a turbine. The compressor uses forced induction (increased air pressure on entrance) to increase power and efficiency depending on the setup.