ok guys let me explain what back pressure really means...even a well-designed muffler will produce some back presssure in the system. back pressure reduces an engine's volumetric effiency, or ability to breathe. escessive back pressure caused by defects in a muffler or other exhaust system part can slow or stop the engine. however, a small amount of back pressure can be used intentionally to alow a slower passage of exhaust gases through the cat converter. this slower passage results in more complete conversion to less harmful gases. also, no back pressure may allow gases to enter the exhaust.
