The ST Sound-Core is a patent pending technology from aFe, compatible with MACH-Force ST and Takeda ST exhaust systems . With this technology, you can easily modify the sound and tone of your exhaust system. By placing the ST Sound-Core in between the two stepped V-band flanges in the exhaust system, you can control the amount of flow that is bypassing the muffler, and change the overall tone of the exhaust with the unique reflection-chamber design. With a medium diameter ST Core, you can provide a powerful tone on the street, and remove the ST sound core for wide open full volume. The ST Sound core provides the benefits of an active exhaust system without the need for an exhaust valve.