Davidn,
Scott and other have it right. Nothing larger than 1+3/4 or 1+5/8" is max if you are looking for gas mileage. Add H-pipe if you want smooth sound. Individual pipes if you want the rap sound. Move mufflers back as far as you can to move the sound back. Mufflers are your call. Many like glass packs, go for stainless pipes and mufflers to do it once. good luck
