The key is speed performance exhaust back pressure

While the four-stroke combustion engine originally designed completely, but the more cylinders automobile, no separate exhaust duct of each cylinder, as well as consideration of noise, space, cost of production and the overall configuration of the exhaust pipe is simply the muffler and exhaust gas cooling purposes, so there will be smooth enough problems, thereby reducing the performance of the engine should be.(subaru coilovers) So rather than describe the modifications that increase horsepower exhaust pipe is, it is more horsepower to get back and play the original output more appropriate.
Patency of the exhaust pipe , that is known to everyone "back pressure" of the term , or can be called back pressure , back pressure , in short it is the internal resistance of the exhaust pipe , which banana head design and Pakistan , the middle diameter thickness, the overall length of the catalyst , corners , silencers size has an associated cylinder , while the exhaust directly reflected in the performance . The main purpose of the amendment is the modification of the exhaust pipe to reduce exhaust back pressure to allow cross- Pa suck more fun , but it also belongs to a disguised extension of valve overlap time to enhance lung capacity , so you can change the engine characteristics , thus enhancing response and high power transfer domain .(turbochargers)
However, the back pressure is not to say the lower the better, because if excessive exhaust unimpeded , then low rpm mixture would simply not have been complete combustion exhaust , torque is bound to sacrifice , even when the oil return pipe when the pressure becomes low , and the exhaust gas back to the combustion chamber countercurrent possible, so a back pressure is still required .(turbocharger for sale)