Like a fire extinguisher in your house, or an earthquake kit, it's always better to be prepared. Although rare, Diesel Engine Runaway is caused when external hydrocarbons are drawn into the engine and can cause over speeding and catastrophic engine failure. Life, limb and your vehicle are put in jeopardy. BD Diesel Performance has you covered should the worst happen with our Positive Air Shut-Off (PAS) by cutting the intake air supply to the cylinders and safely shutting down the engine. The Positive Air Shut-Off butterfly valve design simplifies the number of parts and reduces the overall size as compared to competitive units and uses aluminum and stainless components plus weatherproof electrical connectors to prevent corrosion. Easy installation with bead boot locks - no need for welding. CAC pipes included for some vehicles.