Everything works together, so it depends . . . . I've seen numbers up in the 290's or so depending w/ gt40P heads and intakes, but really it also depends on what else you do (cam, valvetrain, MAF, CAI, throttle body, exhaust etc.). Just the intake I think I've heard like 15 hp, enough to notice, not sure what just the heads and intake and no other mods would make; maybe like 250-260? but you'd hit bottlenecks that would hold you back from making more power than that if you didn't do everything else too . . .