Personally I wouldn’t know.......BUT I’m led to believe the ISF manifolds were a weak point in manufacturing, again I’m absolutely NO expert BUT as far as I’m aware Lexus corrected this weakness on the GSF manifolds, both have the same stud pattern layout and use the same gaskets, the increase in BHP is manifold configuration to a degree, I’ve a set of GSF manifolds that will be getting fitted to my ISF at some point due to a small crack in the ISF ones, not sure any power increase will be noticed as the car isn’t tracked or driven in track ways barring the odd burst where time, location and road layout allows.