If I have my hand on the pulse of this forum correctly, most people will say that the 616 and 617 engines of the early 80's (by the way I think the newer engines began in 86 so they are not the same as 85's) are better. They are all iron. The newer engines have aluminum heads which are inclined to warp if overheated. I believe the post 85 diesels have self-adjusting valves but most motorheads are willing to adjust their valves in return for a few more pounds of iron.