That chart is terrible! I think alot of people go overkill on exhaust but that chart is just underkill. my personal thouhts are 2-2 1/4 for 300 hp 2 1/4-2 1/2 for 400 and 2 1/2- 3 for 400+. for turbos i might step up a size in pipe since I hear they spool quicker with bigger pipes. I might run 3 inch if your looking for that loud echo sound ( on a lower hp engine).
