2013.5 – 2024 Cummins ISX15 & X15 Engines. Doctor Diesel USA’s Big Boss Intake manifolds are built to increase and balance the air going into the engine. By opening up the manifold in key areas airflow will increase up to 35% leading to lower air intake temperatures resulting in power gains of up to 20hp. These direct replacement manifolds are simple to install and utilize factory hardware. The address on your account MUST be verified. All of our parts and accessories are returnable and refundable. The item MUST be unused, uninstalled, in the original packaging and in brand new condition. We value your business and we are not satisfied unless you are. Welcome to Doctor Diesel USA.