Random block plug next to freeze plug?

[verSat1l3]

So I'm reassembling my s14's ka24de and I noticed that the machine shop forgot to reinstall the block plug on the exhaust side of the motor. Its located just to the left (front of motor) from the rightmost (rear lower) freeze plug. I pulled the plug from my spare s13 block and used it, so problem solved.

My question is what exactly is this plug blocking? Is it an oil or water passage or what? I can see the exterior of the bore chamber inside the passage when I look in the plug hole. When I look inside the block from the bottom where the crank sits all I can see is the wall of the block that runs into the bores. There's no related passageway to the plug on the inside. The oil squirters are on the other side so it doesn't appear to be the same chamber as those. Any ideas?

Sorry I dont have any pics and my roommates digital camera broke. I can draw a quick diagram if no one can figure out what I'm referring to.

[mach5camaross]

water galley in block