If you are climate conscious, cat-back exhaust systems (short for catalyst-back exhaust systems) could fit your needs. There are many such after-market cat-backs. [Catalystic convertors reduce the harmful hydrocarbons and heavy nitrogen gases produced by the engine to (slightly) less lethal gases. The more the number of cats, better pollution control.]

These cat-back exhaust systems leave the emissions-control gear in place, but allow you to put large-diameter exhaust pipes and low-restriction performance mufflers into the system after the catalytic converter.
The net result is lower auto exhaust backpressure, more horsepower, more torque, and a much hotter sound, all while staying perfectly legal.

To see the parts and functions of an exhaust system try the diagram below:
http://www.kwik-fit.com/assets/jpg/g...work_large.jpg

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