This unit replaces the factory 2" mid pipe. This will bolt up to stock components or aftermarket. For best results exhaust size should be matched. This section has 3 bends, a flex section and the rear (secondary) O2 bung. Upgrading this section of the exhaust does not affect emissions. This can be upgraded by itself or along with other sections of the exhaust. Upgrading this piece gives 3-4 HP. It does not require any type of tuning.