Im no expert on the NISMO parts but S tune parts are less mean. They unclude exaust, thicker sway bar, and a suspension kit (they have floor mats a decals and what not too but I am talking performance.) R Tune is heavier...FPR, CAI, Header (w/ and w/ out a cat), brake pads, rear sway bar and my personal favorite...cams, mmmmmmm. Hope this site helps.--Zac
http://www.courtesyparts.com/nismo/b15/