S cover , ? cover , 50 trim , 70 trim , what does it all mean ? is there a so called ' bible ' such as there is available for the small block chevy , that answers all the questions one would have , if he were trying to figure out which turbo would best suit a particular application ? i mean really , how are u suppost to know even what / where to start looking at as far as the spec.'s for a new whistle ? do you start by looking at the horse power it produces , and where you are going to drive it , like stock replacement / upgrade , street / strip , race , etc...need info / help to make the right choice the first time.