The word backpressure, in an exhaust system, is the amount of reverse pressure, or resistance to flow of the exhaust gases, imparted by the various exhaust components. The less backpressure there is in your exhaust system, up to a point, the better your engine will work. There are a variety of ways to accomplish this. Some of these are cat back high flow systems that replace everything from the catalytic converter back and header back systems, which also replace the catalytic converter with a higher flow model. The next step is to also add headers in place of the standard exhaust manifold(s).