Downpipe.

The downpipe is between the turbine exhaust and the catalytic converter. The stock pipe on the 2g cars is 2". Most replacements are 2.5" and 3". Obviously enlarging this pipe further reduces backpressure in the exhaust system. Lower backpressure allows the turbo to spool up quicker, allows higher boost levels, and reduces stress on the turbo. There realy isn't much involved in this mod. If you are going to be keeping you catalytic converter then be sure to get a downpipe with a flex section. This will limit the engine vibration transmitted to the rest of the exhaust system. Some DP's are even polished to a mirror finish. Although this won't make your car go faster, it does look really nice at the car show :)