Stage 2 is the common cam for a 660 and may need springs. Stage 3 is normally for built motors like more compression, big bore, bigger carbs, intake and exhaust mods. As said though, start with the "Big 3" first. Intake, exhaust, and jetting. You should notice at least a 5HP increase. Next would be a cam, and they like more compression.
2007 RAPTOR 700, SAND QUAD, 66HP @ OCP. CUERVO +1 HEAD, HDD 5050, 11:1 CP, +5 HR, PC5, DMC FORCE 4, +2 TB, FCI, LONE STAR XC +1, HD TIE RODS, CCP, WORKS, JOKERS +1 STEM, RDZ CHAIN TENSIONER, ASV, +2 1/2 FACTORY SWINGARM, +4 ALBA AXLE, +2 REAR HUBS, DR.D, ODI, 1 1/8 CARBON BARS, DG BUMPER. GYTR: BRAKE LEVER, SHIFT LEVER, NERF BARS, HEAL GUARDS. BILLET: GAS CAP, BRAKE COVER, THROTTLE LEVER, OIL DIPSTICK, BAR MOUNTS. LED LIGHTS, FLUIDYNE RADIATOR, GRIPPER SEAT, 3 OHM COIL, PLUG WIRE MOD. 1.6 CAP