Rear exit exhaust systems are designed for clearance of an original size spare tire mounted underneath the bed. If you have an oversize spare, it will have to be removed to use these systems.With 2-1/4" tailpipes, these dual exhaust systems reduce exhaust restriction and back pressure for increased horsepower and better fuel economy. Complete with bolt-on connectors that adapt to your stock manifold ... no welding necessary! All parts and hardware for standard installation are included. The standard stock exhaust system of a truck with a 360 engine is a single 2" pipe. This means that you will be getting a 125% increase in exhaust flow, increasing horsepower by up to 18% and improving fuel efficiency and low-end torque at the same time. Increases in fuel efficiency and horsepower are based on a truck operating at factory specifications. Increases may vary according to the condition of your truck and driving habits. Manufactured from 16-gauge aluminized steel that lasts up to twice as long as conventional plain steel systems. Made with modern tube benders utilizing mandrel bends ensuring each bend is smooth flowing increasing exhaust flow by up to 20% over stock systems.