all the tuners I have talked to they seem to pretty much all say that "SAFE" hp is around 500 fwhp with 87-93 lines and rails and 550 fwhp with 94/95 lines and rails. These were supercharged applications with a higher bsfc so there is some different factors that go into the figuring out different fuel system requirements. The 94/95 lines and rails are marginally better then the older style of the foxes and is used by some as a cheap improvement to the foxes. People obviously have gone past these #'s but the key word is "safe". IMO once you get past 450-475 rwhp it's time to start thinking about a larger external pump, larger lines, and larger rails to support the volume of fuel needed to support all 8 cylinders with adequate fuel.