I can only run a 3.25 pulley with my mods. Keep in mind the XP bleeds off some boost so without the cam, a 3.4 with too much fuel and lowered timing was the best I could do with modded 1.9 rockers. It's more important to get a good AFR and ~17 or 18* of timing and then find the right pulley to make those other two things happen without knock.