stock pipe is 2.14" OD, crush bent pipe. If you are runnning an N/A i would suggest upping it to 2.5" pipe mandrel bent from the cat back. You should notice a big difference. If you are Turbo, go 3 inches or bigger. The bigger the better with a turbo, since you are just trying to get the exhaust out while the snail pumps more air in, with an N/A you need back pressure for proper cylinder scavenging, so going to big is a bad thing, but typically half an inch over stock piping is the way to go because you wont loose to much back pressure but will see an increase in airflow through the engine = more horsepower.
