Oil pump selection. HV/HP or HV/ normal P
 

I am re-doing 540 BBC engines. Bearing clearance is .0028-.003 on rods around .003 on mains. I am installing Melling High Volume oil pumps. They came with a high pressure spring installed, but also had the "std pressure" spring in the box with instructions. Normally in my drag (car) engines I like the HV pump with the std pressure spring to reduce the load at high RPM (7000 or so). But the engine only sees limited run time and is rebuilt every other year. I am planning on running a max RPM around 5200 in the boat.
SO, the question is, which spring should I install in the boat engines.
I would think that a little more pressure would just be insurance rather than a big parasitic load.

i always run the higher pressure,it makes up for the xtra hoses and oil cooler.

Mike,
I am on the same page, but had been getting mixed advice from fellow motor heads. Parasitic loss vs lower pressure. With all the plumbing and restrictions in the Merc system, I am thinking it is better to have a bit more pressure. But since I am a novice, I am willing to listen to others suggestions.
Thanks for the input.

I'm running the 10778c w/ high pressure spring. They say the anti cavitation feature helps keep timing stable at wot rpm so that is why I use it. I also run larger clearance like yours and appreciate the extra flow to keep bearings cooler.

the parasitic loss is not noticable in a boat,but your engine will like the xtra pressure.

there is so much wrong with this reasoning in this thread , its hard to know where to start...

" clearences around .003 " you don't know ? simply the single most important number on your whole assembly and its a guess ?

and the "more is better" is just nonsense. if you over volume or over pressure the sytem you simply drive the bypasses open non stop, pump heat into the oil for no gain, and wear out the cam gear with the additional drag.

it is a common novice mistake that is supported by folklore and continually handed down by theads like this.

the simple hardcore unassailable fact of the matter is that unless you have increased the mechanical loads in some material fashion such as supercharging or increased revs extremely high static compression ratios, or you were really stupid and put big crank clearences in it then the all thats required is the oil pump and spring that it came with that gave you 50 psi hot at off idle revs. everything after that is wrong to some degree.

i simply do not understand why every conventional big block bottom end that gets built on here has to be reinvented as if the formula for the clearences and pressures hasn't been a matter of absolute fact for 50 freaking years... what exactly is it that has suddenly changed from what has worked forever ?

I use high vol/high pressure pumps and my oil temps are perfect, no appeciable wear on cam gears and bottom ends alway look great. This is with supercharged engines. So this works too. So who peed in your weaties today xmsteve?

no one... but as i said, i simply don't understand why it is necessary to reinvent the basics every single time.

there is a very basic and fundemental premise upon which all engineering in every discipline is based... that is

" what's right is right and everything else is wrong to some degree " hi volume oil pumps and ultra hi oil pressures in low stress applications are the wrong thing to do. period. end of discussion. there is no upside to it at all and all manner of potential downsides. why do something wrong when you can do it correctly just as easily ?

in this instance you have a very basic and fundemental , low stress bottom end. and what do you see ?

no idea what the most important clearence in it is. yet...the question revolves around a component selection and specification that is already answered by by what he has been running successfully.

thats the SECOND basic rule of engineering...

never fix anything that isn't broken.

i can see the thread now... " gee, i just rebuilt my motor... i think the clearences were somewhere beween zero and 1 inch and i have 240 lbs of oil pressure sometimes and zero others and then it blew up. i think it was the fram filter i was running . do you think i need a bigger oil cooler ? "

it is the ongoing saga of the self inflicted disaster. it starts with " this " thread 10 out of 10 times.

and i'm still wondering if dr ratz ever got in touch with the space aliens that were beaming his oil pressure to pluto every time he gets to 4000 rpm...

This is a hobby stevexm for most of us. That's how hobbies work. You comingle and learn slowly as you go from more senior hobbyist. If it were a business (for profit) we would all go buy a merc hp product and be done with it. 1/2 the fun of a hobby is stretching the conventional norms and learning as you go. Engineering our own solutions. That is fun to many of us. I can also tell you from being an engineer for over 25yrs grass roots practical hobbyist often have a better handle on what works for max perf. Engineers have many more business related constraints than hobbyist and are more limited in thier approach for this reason. That's why having an open mind on forums like this can be positive to even the most seasoned professional, whether they will admit it or not.

Completely incorrect from an engineering perspective. The second basic rule is to question everything. That is where innovation resides. We'd still be riding horse and buggies if everyone took your approach.

Hmmm....i was always told (Back when i was in school)it was

1. Make sure its safe
2. Keep it simple
3. Explain it clearly

:D ;)

WOW !!!!!!!!!!!
I shouldn't have too, but I think I need to defend my level of expertise.
As a matter of fact, I agree with stevesxm, bearing clearance is one of the many important parameters in any engine, and yes, I do know exactly what each bearing clearance is, but decided to skip that level of detail, but rather give a general description.
I do appreciate the input from all who have gone before me, expert or novice, which most of us are and want to learn from other's mistakes and experiences. As for rules and re-inventing best practice, I am old enough to remember when roller cams were exotic and front engine dragsters were state of the art until someone tried something different. If it wasn't for creative "average Joe's" there would have never been a chopped, fender-less Model A Ford with a decked flat head engine in any other color than black.
Point is, I will end up making the final choice on oil pump pressure. I find this forum a very good place to get information and hear about other people's experiences, Pro's and shade tree guys alike. The more you know, the better. Thanks guys.

i've always been told that the chevy pump is plenty good for stock and most builds...but hey,what do i know....im a harley mechanic

fyi,the pump in question can produce app 250 lbs pressure,on all oil pumps,the releif valve opens and control,s the pressure,in my opinion,any marine engine will benefit from the addaquit pressure from useing the higher pressure spring.a marine engine gets run at higher rpm range for long periods of time compared to a car engine,it is not uncommon to run a marine engine at 4000 rpm for extended period of time,unlike a car that runs at app 2000 rpm at 70 mph.maybe the engineer who decided to include 2 springs has no idea about what he is doing!