Intake kits are performance parts that increase horsepower by replacing the factory restrictive airbox and air filter. Intakes come in two types, short ram and cold air. A short ram intake is a short piece of pipe with an air filter element on the end. A cold air intake is designed to suck in air from outside the engine compartment so that the rig can get cooler air more densely packed with air molecules. The vehicle ECU compensates for this denser air by adding more fuel, thus creating more power. If you have modified your engine you might consider replacing the stock throttle body with a larger one to create the amount of airflow that matches the horsepower that your modified engine can achieve.