doctor_ratz

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.

mike tkach

iTrader: (3)

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

doctor_ratz

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.

blue thunder

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.

mike tkach

iTrader: (3)

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

stevesxm

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 ?

blue thunder

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?

stevesxm

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...

blue thunder

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.

blue thunder

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.