In addition to increasing gas mileage, aftermarket exhaust systems have the added benefit of increasing horsepower, drastically in some cases. Gains in fuel economy alone are worth adding aftermarket exhaust systems to your vehicles. However power gains can also make this modification quite attractive. Restrictions in exhaust systems create backpressure on the pistons in an engine. This backpressure puts an unnecessary force on the piston top slowing down its movement and robbing your vehicle of precious horsepower and torque. This extra energy is essentially wasted and is the source for gas mileage drop, loss of power, and acceleration.
Aftermarket exhaust systems including headers, high flow catalytic converters (CAT), less restrictive mufflers, and mandrel bent exhaust tubing of larger diameters can significantly enhance a vehicle’s power. All mentioned modifications serve to reduce exhaust gas backpressure. The end result is the same but the extent to which each part affects gas flow varies.
One of the most restrictive parts of a car’s exhaust system is the stock exhaust manifold. Typically made of cast iron these parts are much heavier than their header counterparts. This adds additional weight to the system robbing power and mileage as well. Headers are usually manufactured from stainless steel or aluminum, many times also being coated with ceramic paint for heat reduction. Aftermarket headers greatly increase the flow area as compared to exhaust manifold systems. Not only are the ports attached to each individual cylinder larger in diameter than with manifolds, but the length of the header tubing attached to each individual cylinder exhaust port is also much longer. The effect is an enhanced ability to flow exhaust gases out of your motor and reduce engine temperatures as well. There are many aftermarket header companies including BBK, Hedman, Pacesetter, Flowtech, Hooker, ASM, and Summit to name a few. Headers can be quite expensive and there are many different options. As usual make sure you do plenty of research before purchasing a particular model, so that you know what you are getting into. Power gains vary wildly between brand and style of header. However gains of between 0 to 40 horsepower and 0 to 30 foot pounds of torque can be expected.
Mufflers are the bread and butter of an exhaust system. Their purpose is to quiet down exhaust tone as well as absorb much of the heat from exhaust gases before they leave the system. Stock vehicle mufflers are quite restrictive! In fact gains of between 5 and 20 hp are not uncommon in certain applications when replacing a stock muffler. There are many different aftermarket muffler designs utilizing different materials. Some have a central, perforated flow tube surrounded by fiberglass matting; others have no matting at all but multiple internal chambers or baffles which direct exhaust gases in specific ways to produce desired effects. Consult multiple sources before purchasing a high flow exhaust. Companies include but are not limited to Magnaflow, Borla, Flowmaster, Thrush, Dynomax, Gibson, and Walker.
High flow catalytic converters were previously mentioned within the fuel economy tips section. Their main function is to convert some of the harmful exhaust gases such as nitric oxide, carbon monoxide, and hydrocarbons to carbon dioxide, water, nitrogen, and oxygen so that they do not harm the environment. This is a chemical reaction that occurs within the catalytic converter when it reaches a certain optimal temperature. While performing a valuable duty for the environment and human health catalytic converters are also very restrictive to exhaust flow. However some companies sell less restrictive “high flow” cats which provide better flow but still perform all the necessary functions required to pass emissions.