You might as well upgrade the whole header-cat-exhaust system. However you should first determine your long term power goals, then get the parts. Otherwise down the road, you might need to get larger piping to extract the most from bigger cams/displacement. 2.5" piping throughout should be good. However, most Japanese exhaust manufacturers make 2.38" exhausts, which could be restrictive only if you have like 230+whp.