with a d/v fitted apparently will help prolong the life of ur turbo as will a decat system. I cant understand how the dumpvale will make the car over fuel as posted by the squirrel555, excess fuel will not be able to run down the cylnder walls in to your sump past compresion rings and oil seals instead it will exit via the exhaust port and backfire in the exhaust system. And i also cant see how it will cause the car to run lean as posted by zeolite as a dump valve has nothing to do will the fuell system, plus there must be benefits of the slightly heated manifold pressure being dumped to atmopsphere, and a fresh intake being drawn, hope i have not offended anybody and im only trying to have a better understanding of this.