1) Exhaust manifold. Exhaust manifold is generally the most expensive part in exhaust system modification. Due to the strict requirements to the length, diameter and blind bend, so its production and development costs are high. However, whether the exhaust manifold design excellent or not plays a very important role to the exhaust system.
2) Three-way catalytic converter. The three-way catalytic converter is an important equipment to control the harmful gases, mainly to purify the hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOX) and other harmful gases in engine exhaust gases. In order to minimize exhaust resistance, there are many suppliers forced removal the catalytic converters, which will not only causes vehicle emissions excessive, but also make the cars ECU which parts have self-diagnostic functions send some wrong signal, so affecting the normal traffic, therefore it is the best to retain the original car's catalytic converter. Now there are lots of new three-way catalytic converters will not hinder the flow rate of the exhaust gas. So, you can change a dedicated high-performance catalytic converters, but the higher prices.