Compression test question

I consider naxja to have the best knowledge base of all the forums. That being said I am working on a 3.2 cadillac, and replaced the heads(Had them professionally rebuilt, new valves guides etc) new timing belt, properly timed. I am conducting a compression test prior to starting. 5 of the 6 cylinders are reading 180-200, but the back right is reading 270, consistently. I am at a loss, does anybody have any ideas, why one cylinder would be higher than the rest? Two thought i had were water/oil in cylinder? But i cycled it several times with spark plug out. Or a lifter issue? Thanks guys!!

I have no solution(s), only speculation(s), and question(s).
1) Usually, a high compression in one cylinder over the others indicates carbon build-up on piston. You think a possible problem is with a valve not working properly which I guess could be your exhaust valve is always closed during cycling. To me the easiest way to check that is to pull valve cover off, and see if that rocker is not cracked, (doubtful), and while cycling engine to see if the rocker pivots evenly, as the others, and watch to see if there is a difference from the others as per whether the push rod ends, and valve stems move properly, i.e., up, and down, etc. Should show if an exhaust valve split keeper(s) became dis-lodged, or a dead lifter by observing the actions of each underside ends of that rocker as it pivots.
2) Did you by perchance leave a rag in the cylinder in question when reinstalling head?

I have nothing else.

I found out the problem. I had water in the cylinder. It was raining(I was under partial cover). The rain was dripping down the windshield and into the spark plug hole. I cycled the engine several times, I could see the water vapor coming out. After. That compression test was normal.

Here's another tidbit I learned, for what it's worth. I finished all engine work, rebuilt heads, new timing belt, head gasket etc. checked oil, good level. Added coolant. Keep in mind good compression test. Start and run engine. Doesn't sound right.

So I start poking around, open oil fill cap to see the valve train. What do I see instead? Coffee colored oil. And this after only about 3 minutes of run time. I was a lil freaked out, as I had followed head torquing procedures to the letter, used high end felpro gaskets. I shut engine off went inside. I thought about it alot. Didn't make sense a head gasket could leak that much water in such a short time. Then I remembered the engine had been without heads for over a week. And while I had the hood closed. It still managed to leak water. Right into the oil passages and into oil pan. So after a few oil changes, all was well. A lesson I learned, maybe can benefit somebody else.

Sheesh.., if it wasn't for bad luck you might not have any luck at all. (Pig Pen of the Grateful Dead). Once did a six banger head job in a snow flurry, and did not have your luck, lol. Thanks for the update so we can chalk that one up. I can see that happening on cyl. #6 with the hood up in the rain, and taking a long break before installing head on a six banger. Best to take a last look on the tops of the pistons. Your Caddy issue is different in how water made it into your engine though. Thanks for the feed-back.