I want to finish my exhaust . I got true duals from the cats back was noticeing that my stock manifolds look very restrictive and small y pipeing . i heard shortie headers dont give that much improvement on the LS motors but would a set be good on the L31 ? Also most shorties have 1.5 inch primaries i found a few with 1 5/8 pirmaries and 2.5 collector would the bigger primaries be better ? I will be up gradeing the y pipe also to a 2.5 inch with some new 2.5 cats , what cats would you guys recomend ? thanks.