The case "press in plugs" were removed and the case tapped to 3/8"npt (x5). Do I need to use SS plugs or will the cathodic/anodic ratio (CAR) allow me to use yellow brass plugs? Four of these are clustered. I suppose heat and oil movement will come in to play as sources of energy and accelerate the action?

Well Mr. Corrosion Engineer ... check the table ... shit forgot what it's called ... oh well ... the one that shows the potential for corrosion when two metals are mated & pick the ones that are closest together.

I thought most shops just used steel.

Ah hah .... Galvanic Corrosion .... Galvanic Corrosion Chart

I'm no expert but I would perfer Aluminum plugs for the best expansion and contraction match. I would deduce that's why the metal plugs eventually loosen and pop out. But that's just my WAG. I really don't see a reason why you can't use brass also.

some time in the past, I acquired an engine case in with a bunch of parts I bought from Motorsport (he close up business )

it has brass plugs, sooooo....

rick, alu to alu has galling problems. Steel don't leak. done

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Then that would be SS. Actually cadmium plated would be the ticket. Thx

Even with galvanic corrosion being better between stainless and aluminum, I would think that the expansion of stainless would be a bad thing. I had got the stainless plugs from summit I think, but they were much longer, deeper than the black oxide steel ones that I got at rimco, so I used the black oxide ones.

Baker Precision I think it was sent me some aluminum ones when I ordered steel ones from them - they didn't know the difference? From the research I did, aluminum ones will never come back out, so you can't clean out the galley ever again during a later rebuild.

Galvanic chart my ass. You're thinking too hard. The loser of any galvanic action would be aluminum, of which your case has about 50 lb. So your 40 lb case is going to corrode away as a result of a few little plugs? Why wouldn't already be corroding as a result of contact with other iron parts?

You're going to tap with pipe threads that'll give tight interference, plus thread sealant. Use whatever material for the plugs, just don't turn them in so far that you block the oil galley.