I'm putting a late model 5.0 in my 70 mustang and don't know what this is. Its on the top of the back of the block. Not sure if its supposed to be plugged or not......any help would be appreciated.
If you're talking about the black round thing, it IS a plug actually, a mini block freeze-out plug except it blocks oil from escaping, if you took it out you would see (at least on my 302 anyways) 2 passageways going down, one to the left side, the other going to the right(from what I remember.) I believe it's how Ford designed one of the oil passageways? they drilled the two holes within one hole so the oil could get to the other side and not have a whole mess of holes in the block and they just put the plug to seal it all up (not all the way in or else it would obstruct the oil flow), but just a guess there.
Same method is how they make some of the passageways in dirtbike/quad/moped etc. carburetors though, they drill holes all the way through the body and intersect the passages with other ones and plug the outside holes and Voila instant internal passageway.
thanks for all the responses....I finally got ahold of my buddy who built the short block and he told me that it is/was for a knock sensor and nothing needs to be done with it.