RD Series Race Division Intake Systems The RD series is a cold air intake system for the enthusiast craving mid-range power. The intake tube is strategically placed behind the front bumper to acquire colder, denser air. Although most of the RD series is a one-piece design, several are two-piece designs due to the mass air flow meters. Every RD system is certified or pending by the California Air Resource Board and backed by Injen Technology's limited lifetime warranty.