Catalytic Converter Eliminator from M4. Fits stock mufflers and most aftermarket mufflers. Removing the catalytic converter produces more power and reduces heat under the seat. Comes with O2 bung adapter to fit stock or aftermarket O2 sensors. Note: M4 Recommends re-flashing your stock ECU to unleash the full potential of all M4 products. Note: All M4 systems are designed and intended for closed-course competition use only.