Close the raw water intake for compression test?
 

Curious if any of you do this? I'll be testing the compression on a 5.7 Black Scorpion in 11 hours.

This is the only part I am wondering about, apparently this is done whenever cranking on an engine, without starting it, because:
"most marine engines use a water lift exhaust system. The Water Lift system uses exhaust pressure to push cooling water out of the water lift up and through the exhaust system. Without the engine running, there is no exhaust pressure to push the water out. The water will eventually fill up the exhaust manifold and then the engine itself. Although not fatal to the engine, it is a real hassle to correct."
http://www.moyermarine.com/forums/showthread.php?t=7396
and
http://forums.sailboatowners.com/ind...arting.113358/

Maybe it is not needed for the 30 or so cranks I need to make?

I'm a little confused as to what your asking with all this mumbo jumbo. For a compression test, all you need to do is pull a spark plug and put your adapter/gauge on and crank over the motor 2-3 times. It's best to pull the fuse for fuel pump so the motor won't start. It's easier that way. The way the risers are made there is no possible way you can suck back any water through the manifolds. You can do this in the water or on the trailer, it doesn't matter which.

In a word no doesn't apply to Inboards you will need to disconnect fuel as mentioned open throttle wide open and stick compression tester in appropriate hole BTW some fly by wire engines may need to be put in special diag mode for compression check

This is want happens when you search "Marine Engine compression check" - you wind up on some page that tells you "most marine engines need to have the water intake plugged" Anyway, I thought that was not needed. So, you can do the compression test in the water. What happens if you forget to unplug the multi port injection system (or cant figure out how), possible flooding or worse?