here is my opinion: I have an XP cam, ported heads, a full size intercooler and am running a 3.25" pulley. my car has kr when I go smaller. you will not be able to just buy one pulley and call it good, unless you are will to settle with a 3.5". you could probably run a 3.25" pulley if you did the headers 1.9 rockers and a methanol injection, but again tuning will be required.