The Holley kit comes with a single wideband Bosch oxygen sensor and a weld-in bung for it. You can mount it on either cylinder bank if you are running true dual exhaust. DC Performance mounted ours right at the passenger-side header's collector. As an option, Holley offers an NTK sensor that can handle nitrous or leaded race gas. Since we weren't running either of those and the NTK sensor is considerably more expensive, we went with the Bosch unit.