Ray , I've used Melling HV pumps on all big blocks in the past in all Ford or Chevy engines. Consistent pressures with small drop at high temps., rock solid when cold at idle.
Can't say the same for my bone stock 377 sbc since day one ,and I have only around 200 hrs on both engines. SmartCraft and analogue backup gauges both read around 40-42 pressure at 600 rpm when cold , and drops as low as 27-28 when the oil is hot .Should have an oil cooler on these . I've been using the Merc 25-40 blend from day one , and wonder if it would be better to switch for 20-50 .Which oil would you recommend for this 6.2 MX [377] engine? Thanks
Ps; the stock oil pan is quite small and I wonder if the oil splashes up the cylinder walls running hard in rough water ,causing the oil getting too hot .

I have a M77HV in my starboard engine and a 10778c in my port engine. I forget which one does it, but at idle one engine bounces between 30-50lbs every once in a while. normally runs 80lbs cold and 50 hot. I think it is my port engine.

All else being equal i.e. same bearings, oil lines etc, does switching to a HV pump raise oil pressure?

Yes about 6 to 10 psi. But you do not want anything over 65 - 70 psi cold idle.

I run the melling HV that was purchased then sent to another shop to be blueprinted. works very well but does fluctuate at hot idle. just my 2 cents.

What's the issue above 65-70 psi cold idle??

I rebuilt 500HPs several years ago and have had 45-50 psi hot WOT and 20 psi hot idle ever since. Don't remember the cold idle pressure.

Both engines out of the boat now and the bearings/leakdowns look good so I was going to add a HV oil pump to boost the pressure a little. Looks like the lower oil pressure is due to clearances from the rebuild so a HV pump could make better pressure?

Does the pressure fluctuate with rpm at idle i.e. blower surge or cam lope???

Why is that? Every engine that I build has more than that at a cold idle.

Not so much with cam lope, but pressure will move around with any pump if the rpms are surging up and down do to a blower, etc.

Cold High Pressure
 

Eddie, We found on alot of our Road Race engines that run heavier weight oil, that the higher pressure with "cold" oil was showing signs of bearing erosion happening. (Sort of like trying to push clay through a pop bottle). We alway blue print the pump and adjust the spring to maintain the idle pressure at about 60 psi based on the oil that is going to be used in the engine. Most of the bearing erosion will happen from high oil pressure at start up's. Cold oil as we know does no good to the engine either, then to run high pressure on top of that?? A engine really only needs about 5 psi per 1000 rpm (even though most people use the 10 per 1000 rule of thumb). Just for what it is worth. Pete