Yes. The tuned exhaust system must be designed for a .21-size engine and be intended to be used in your type of R/C car. It also must fit into the car. Tuned systems are usually RPM specific for the top RPM, so you need to use the type for your car. An on-road oval-racing car that runs mostly at full throttle will use a different pipe than will an off-road car that's on and off the throttle a lot.