So what would be the most amount of boost to run without increasing fuel? you won't get boost without fuel. It is all relative. you could wind the boost up as high as you like but since diesels don't have spark plugs they need the correct ratio of air and fuel to make horse power. Up the boost, you ...

I have a 1995 Nissan terrano r3mr with a td27eti motor. It runs 12 pounds of boost standard hope that helps.