Derestricting your vehicle's stock exhaust offers numerous performance benefits. A higher-flowing exhaust system allows the engine to more efficiently expel exhaust gases. This improves both the peak horsepower numbers and fuel economy of your engine. Some stock vehicle exhaust systems have exhaust restrictors, which can be removed to increase the exhaust flow. However, most engines require upgrading the exhaust to a system with larger-diameter piping to fully derestrict the engine's exhaust flow.
Use a floor jack to raise the exhaust-side of your car, and support the chassis on jack stands. If you are modifying a motorcycle exhaust, remove any exterior panels restricting access to the exhaust bolts and flanges.
Remove the two bolts securing the muffler and axle-back piping to the rest of the exhaust system. These are connected to a flange just in front of your vehicle's rear muffler. Mounted to the sides of the muffler are metal hooks, secured to the vehicle's underside via rubber hangers. Detach the rubber hangers from the vehicle chassis, and lift the muffler assembly free.
Remove the rest of the exhaust piping up to the catalytic converter by removing all exhaust flange bolts and detaching the rubber exhaust hangers. The cat-back piping leads into the stock muffler location, and attaches to the catalytic converter midway up the vehicle. This section of the exhaust system may be in one piece or several, depending on your vehicle's make and model. Each exhaust segment is secured to the next via two exhaust flange bolts and an exhaust gasket.
Install your upgraded exhaust system in place of the stock exhaust by the opposite procedure of removal. Aftermarket exhaust systems are designed to follow the stock exhaust path, allowing for a direct bolt-on replacement. Place a new exhaust gasket at each exhaust flange connection where any two pipe segments meet. Leave all of the exhaust flange bolts loosely connected until the entire exhaust system is connected to the vehicle.
Adjust the placement of the exhaust system piping so that it avoids any contact with the underside of the vehicle, as this will cause exhaust rattles. Adjusting the exhaust piping will also allow you to properly position the muffler, so that it is centred in the muffler outlet on the rear bumper. Once you've adjusted the exhaust piping into the desired position, tighten all exhaust flange bolts. Get the flange bolts extremely tight to avoid exhaust leaks.
Remove the jack stands, and lower your vehicle. For motorcycles, reinstall all exterior panels removed for exhaust installation.