He said vapor return, not fuel return. Vapor return cannot cause a drop in fuel pressure. All it does is vent the float bowl. Now a solid fuel return is a different story. But properly set up using the fuel pressure regulator as the return orifice, the pressure won't drop, as long as there's enough pump for it. In my case though, there's not an HP mechanical pump for the slant 6 that I know of, so if I run a good return system, I'll have to go electric......which I despise. lol