Valve springs are definitely weak, I personally floated 2 exhaust valves on an 80 shot with APE 47lb springs and .020 spacers. With that said, I am now running APE's 65lb springs with the .020" spacers while ramping in a 200 hp shot, 1 complete season with no problems. Of course, I'm running good rods, pistons, valves, and etc.