to me the real clue was the higher pressure without the merc stuff on the dyno...also I tried a different oil filter and adapter once and lost 20 psi !!!!

This has been a very interesting read for me.....Ok Tom---try not to laugh, this may sound crazy, but as long as you are chasing oddities, here's one for you and probably an unlikely scenario,....but perhaps some stamped steel oil pans can flex slightly? I know there are many ways an engine can be set on the floor using wooden blocks, etc, and this may be a stretch, but is it possible that perhaps when your engine was pulled off the dyno and while setting or as it sat on the floor (in some way) until installed in the boat...and in the process caving/closing the clearance gap between the bottom of the sump and the oil pump pick-up could be enough to restrict the oil pressure...??? Or am I thinking too hard?

You never know. Thinking outside of the box for sure.

Oil flows from pump, to lines, to filter/cooler, than back to block and into main oil galley. If your lines are restricting FLOW, or volume per say to the main oil galley, you would see a reduction in psi there, assuming the oil psi sender is tapped into the block along the pan rail.

On the dyno, my engines had 100psi of oil psi at the main oil galley with a car filter on the block. Once installed in the boat, i have around 75psi at the main oil galley port. This is after its went thru the filter, cooler, lines, which are -12AN.

The other thing to consider , is while the merc lines certainly restrictive, the oil cooler itself, internal passages on the block adapter, and filter head, can also be restrictive. Putting -16 oil lines arent gonna help if the internal passages of those items are the restrictions. This is why companies like keith eickert and others now offer oil coolers, filter mounts, block adapters, with 3/4 NPT fittings. Today's engines are making more power than ever, revving higher than ever, and so on. What once was suffice for a stock 502 or 454, may not be suffice for the modern high power stuff.

i don,t think the op mentioned it but if the block was line honed on the loose side plus crank journals slightly smaller from polishing the clearance,s could be on the big side for a std volume pump imo.edit in.on the flip side,if the line hone was on the tight side the clearance could be tight.

tom,was the oil pump tested on a pump dyno before installing it?

I personally oversaw the movement and storage of the engine... it was never allowed to sit on the pan. Interesting thought though!

No sir.

So yesterday I was chasing a ignition issue that required me to do some rewiring. I did not get the engine started (my module might be gone because it got wet), but I noticed while cranking that the oil pressure was coming up strong on the gauge (25 psi on a slow crank... tired batteries). This was not the case before (the gauge would not move until running), and would lead me to believe that the filter was probably the issue. We'll see next weekend when I play with it some, but this is a positive change. I have yet to cut into the other oil filter, but the oil that came out of it was clean (though somewhat dark from assembly lubes). If I have time tonight, I'll open it up.

Clearances on this build:

Mains are .00275 with #5 at .003
Rods are .0023

The general thinking here is that these clearances may be tight, but I've built them similar with no issues. So long as pressure and oil temp are good, it should live just fine. We'll see.

Regarding oil pressure being 79 psi... I was quoting the exact number per its readout on my dyno paperwork. Let's call it 80 psi from here on.