On my rebuild this winter, I went with the Melling M-77 std replacement pump and replaced the spring with the optional one.

I went with the melling HVHP deal. I've also got a 14qt pan and HV pickup. My machinist told me it's better to run more Clarence and use a bigger pump so that we can keep plenty of cool oil flowing through the bearings. Running a higher volume of thicker, cooler oil through looser Clarence's is better than less, thinner hotter oil in my opinion. He wouldn't set my Clarence's until he knew exactly what weight oil, and what pump we were going with.

I like the sound of the way your machine shop works

Its pretty simple, IF you are running tight clearances (like .001 to .0025) on mains and rods use a std volume pump with optional spring, IF your clearances are closer to .003+/- use a high volume one. FWIW I have my mains and rods at .003-.0035 and used the melling high volume that has the extended pins etc and boat still has 100 lbs of oil pressure cold, even with extra rod side clearance and lifter bore clearance. IF you try to run something like that and your crank/rods are tight you will have problems, IE bypass opening all the time,oil foaming from internal relief opening all the time, blowing filter apart or seal out, accelerated wear on cam gear and distributer gear.

I agree with that theory. While some guys get their panties in a bunch about oil film strength, tight clearances being the modern magic trick, and so on, I personally like the idea of a little looser clearance, cooler running bearings, in a offshore marine engine that sees extended high rpm high load usage. Esp when you start pushing the envelope on power. Just my opinion.

That's my theory also and how mine is set up....

i have to disagree with some of this post,all oil pumps have the bypass valve open most of the time,a standard gear pump can make 200+ lbs of pressure if you don,t allow the bypass to open.i also disagree that a high volume pump will prematurely wear dist gear,if the correct gear is used for the camshaft in the engine and is set up properly you won,t have a wear problem.and if your oil filter is not blowing up with 100 lbs in a loosley set up engine why will 100 lbs blow it out in a tighter set up engine?

who is clarence,lol.

Ha! Stupid phone auto correct!! That's who Clarence is lol

Mike, have you ever seen a motor with tight clearances running a high volume oil pump show 120+ psi of oil pressure, I have and have seen where filters blew orings, were sorta swedged etc. When I start up my boat I run it real easy until the oil warms up and pressure drops to something more reasonable as I dont want to twist off the pump drive or blow anything apart. The biggest problem and its came out in the tech section several times here is a guy bolts in a high volume oil pump on a motor that doesnt need it, there is so much excess oil that the factory block bypass valves open and oil does NOT go to the filter and cooler and things go down hill from there. The factory oil system on most stock mercs has fittings with inside dia as small as 3/8 inch, cant push 8-10 gpm thru it real well, fwiw.