Aftermarket air intake systems are among the most common and least expensive methods to increase horsepower. When it is installed in your Nissan 240XS/180SX, the inlet pipe starts from the top of the engine and makes its way down to the outside of the engine bay, and the air filter is fixed onto the lower end of the pipe. The filter can now breathe the air beneath the engine, which is cooler than the air being brought in by the stock air box resulting in a more powerful combustion when mixed with fuel.