The internal combustion engine requires oxygen to function properly, so optimizing your engine’s intake system to ensure that it gets all the cold air it can use will help to keep the engine functioning efficiently and generating the most power possible. Replacing the original paper filter element with a free flowing performance air filter from a brand like K&N Filters is one of the easiest performance upgrades. Performance air filter elements are made from oiled cotton or oiled foam and drop right into your original air box, allowing your car’s factory air box to perform as well as possible.
Induction kits are the next step. It is possible to install a much larger filter element by replacing the original air box. It is more common to swap out the flat panel for a cone that has a larger surface, either through an enclosed cold air feed, behind a heat shield, or just using the same air supply as the original air box. While a free-flowing air intake may sound better, an enclosed intake system will serve the best purpose of supplying cold air to the engine. Pipes to and from the air box may need to be replaced depending on the type of intake selected.
Choosing an intake filter will depend on what you want from it. When it comes to induction noise, an open cone air filter is most definitely your best bet. When it comes to performance, a cold air feed will be most effective.