stevesxm

pressure and flow are two completely different things....

pressure is a function of volume produced vs volume available.

a pump producing 100 litres per minute into a sewer pipe with an open end will produce zero psi in the pipe.

that same pump put into a close and sealed system will
( assuming positive displacement and no by pass will make pressure to the limit of the mechanicals of the pump and power driving it until it explodes or the power is exceeded and it stalls.

those are the two extremes.

in an motor, the pressure is strictly a function of the clearences and leakage within the system vs the viscosity as conntrolled by the oil temp.

the notion that a bigger or better flowing cooler will build system pressure is nonsense. the notion that putting the filter on either side of the cooler affects pressure is nonsense.
( assuming the position of the sending unit remains constant)

pressure is a strict function of flow vs area to any given point in a total loss system like a typical motor is. if your bearing clearences are big and bleed volume is a large rate then you need a higher volume pump to keep up to maintain the same pressure... IF any element in the system...cooler, lines or whatever can not flow at the rate of the greatest loss in the system then, depending on the position of the sensor, you will either see a acceptable pressure reading ...and fail the engine... or if on the OTHER side of the restriction , see a dramatic pressure loss and ... and fail the engine.

the only parameter that is critical is the total volumetric loss thru clereances and leakage measured in volume/ unit time at worst case scenario vs the total pump output at that rpm .

from that number all you have to do is make sure that the lines, coolers and any other elements in the system have flow rates that exceed that.

now.... who does that math ? answser... nobody. no reason to.

its all been done before and everyone knows that on a conventional big block with bearing clearences that will make the motor live and a conventional hi volume , off the shelf pump with -10 lines or -12 if you are REALLY paranoid, then the oil system is sufficient in most cases. and ALL you have to do is make certain that no port , cavity or oil gallery that runs all this is smaller than that interior area. in fact , however, if you DID the math, you would find that the flow rates of much smaller lines are actually sufficient and that that most of what is done is overkill anyway...

the key to any hydraulic system is consistancy . the flow rate of every element in the system can't be less than the flow rate of the necessary pump at operating speed. no huge lines leading to tiny passages thinking that one compensates for the other... the mechanical system demands a certain presssure at the bearings to maintain non contact float and all you have to do is make sure that nothing in the middle restricts and reduces that . if it DOES then your gauge is actually probably no telling you the truth... it measureing a LOCAL pressure... not a SYSTEM pressure.

it is no more difficult than that.

if your motor made 60 psi at 220 oil temp at 4300 rpm , and you did nothing more than take the cooler ( that was adequate to start with) that was on there off and put on one that flowed 300 % better and was 500 % larger.... it would make EXACTLY the same pressure at exactly the same temp and exactly the same rpm...

folklore not withstanding, thats what physics tells you is true...

and physics seldom lies to you about stuff like this.



so really what we are talking about is reinventing the wheel.

MnHowardCat

29Scarab Your PM box is full
Don

articfriends

[QUOTE=stevesxm]pressure and flow are two completely different things....

pressure is a function of volume produced vs volume available.

a pump producing 100 litres per minute into a sewer pipe with an open end will produce zero psi in the pipe.

that same pump put into a close and sealed system will
( assuming positive displacement and no by pass will make pressure to the limit of the mechanicals of the pump and power driving it until it explodes or the power is exceeded and it stalls.

those are the two extremes.

in an motor, the pressure is strictly a function of the clearences and leakage within the system vs the viscosity as conntrolled by the oil temp.

the notion that a bigger or better flowing cooler will build system pressure is nonsense. the notion that putting the filter on either side of the cooler affects pressure is nonsense.
( assuming the position of the sending unit remains constant)

pressure is a strict function of flow vs area to any given point in a total loss system like a typical motor is. if your bearing clearences are big and bleed volume is a large rate then you need a higher volume pump to keep up to maintain the same pressure... IF any element in the system...cooler, lines or whatever can not flow at the rate of the greatest loss in the system then, depending on the position of the sensor, you will either see a acceptable pressure reading ...and fail the engine... or if on the OTHER side of the restriction , see a dramatic pressure loss and ... and fail the engine.

the only parameter that is critical is the total volumetric loss thru clereances and leakage measured in volume/ unit time at worst case scenario vs the total pump output at that rpm .

from that number all you have to do is make sure that the lines, coolers and any other elements in the system have flow rates that exceed that.

now.... who does that math ? answser... nobody. no reason to.

its all been done before and everyone knows that on a conventional big block with bearing clearences that will make the motor live and a conventional hi volume , off the shelf pump with -10 lines or -12 if you are REALLY paranoid, then the oil system is sufficient in most cases. and ALL you have to do is make certain that no port , cavity or oil gallery that runs all this is smaller than that interior area.

Steve,you are definately very knowledable BUT when you start looking at stock mercruiser oil systems you will see they have rediculous restrictions that will only flow enough oil for motors with tight bearing clearences and stock volume/pressure pumps. It comes up on here OFTEN where someone very new to marine engines builds a nice motor with .0025-.003 main/rod clearences,a high volume oil pump,increased heat load from their mods etc and they have problems with low oil pressure when hot that would be a non-issue with proper sized lines and a bigger cooler (stock stuff is SO restictive they loose 15-20 psi between the oil pump and what they actually have at block). Here are a few pics to show you what I mean,Smitty
I did a huge thread on this last year-Example -stock cooler has holes thare BARElY 3/8 dia ID,cooler is onlt the size of a beer can,adapters with .390 dia fittings plus a dozen restrictive bends that have 3/8 id,block bypass valves that open early due to all the restriction and added load of a high volume pump causing unfiltered,uncooled oil to wipe out bearings,etc

articfriends

More-these pics are of a 3/8 inch dia bolt that fits tight in the stock oil ports

Strip Poker 388

When I ran my powerstrerring pump free flowing [no restriction]there was no pressure.When I ran it thru the filter and cooler still free flowing back into the reservoir it had 150psi.I could pinch the hose and make more psi and if I dead head [pinched]it made 1500 and twisted my arm with the drill With engine running it had 250psi which was going thru the hoses and the helm also. Would this not be a restriction??

Rob



Free flowing zero pressure
http://www.putfile.com/media.php?n=pump-002

Flowing thru the Cooler & Filter 150psi
http://www.putfile.com/media.php?n=pump-011

Picture

articfriends

Yup,sounds like a restriction to me!

stevesxm

artic,
no question you are correct.... and believe that your example illustrates what i am trying to say. you point out that the stock system, as produced , has tight clearences and small lines etc which, while adequate for that specific application are found wanting when you start going bigger meaner and faster.... absolutely true... whats correct for an application is correct. no magic there.

my point is simply that once your sytem is adequately and correctly designed and plumbed i.e correct sized pump and flowrates for the total volume and pressure you need to sustain life at the conditions you intend to operate , then you are home....

if that requirement is -10 lines then -12 lines are not better... just bigger. they aren't going to make more pressure or solve some OTHER problem you have.

its the frog w/ no legs joke.... scientist wants to test how far a frog can jump... yells " jump frog" frog jumps 10 ft. scientist then cuts off frogs legs... yells " jump frog" frog goes nowhere. scientist writes down " frog with no legs goes deaf"

if your motor makes good oil pressure at the bearings except that when the oil gets to 350 degrees the bearings fail, the answer is not to try to get oil that lives at 350 degrees, or bigger lines and pumps... the answer is to get a correct cooler on it so that you oil stays at 220... now did that COOLER make pressure ? no, of course not. the fact that the oil is now OIL instead of lime coolaide is what cause the pressure to come back... viscosity vs area...

and how many times have you seen it it ? guys buy -12 lines and then screw three adapters together to get it to go into a 1/4 pipe port w/ a .25 hole in it ....what have they accomplished ?

i see the lines you are talking about right here on my 502 s and you are correct. they are small w/ tight bends. but do i believe that they will be the ultimate cause of some failure ?

no. at 220 degree oil, 2500 rpm i have 50 psi. that tells me that the system is adequately sized for the demand. could it be more ? sure. but to what end...? at 425 hp, 5000 rpm with stable pressures and temps... what problem am i trying to solve ?

and don't forget.... it is not only POSSIBLE but common to go too far and cause your OWN problem... an oil pump too big will simply push all the extra capacity thru the relieve valve which makes heat in its own right as does having TOO much oil pressure....

you need enough flow and enough pressure to float the bearings off the crank and absorb the shock loads that your motor makes and enough flow rate thru the bearing that the oil doesn't spend enough time there to overheat... HUGE loads in big blown motors.... small loads in low compression low reving motors....

its not one size fits all and not " bigger is always better"

and i have no answer at all why taking the filter out of his ps system would make it go to zero pressure. that makes no sense at all. thats a closed loop zero loss system.... shouldn't even notice whether filter present or not...( assuming its not failed in some other way)

Payton

One more point. It depends on where your sending unit is that is reading the presure. If it's between the pump and the restriction, you will read higher presure than if it's after the restriction. That is why the presure jumped on less restrictive filters and coolers. You eliminated a restriction. The next restriction is the engine block oil clearences.

PatriYacht

Here's where I put the pressure sensor, hole at front of block. I agree with Articfriends that there is value in using larger fittings and hoses. If you were to measure the difference in pressure at the front of the block between a system with the large fittings and one with the smaller ones, I bet it would be substantial. Yes there is a horsepower loss driving any oil pump. I just want to see the high pressure at the bearings and not lost along the way in small, restrictive fittings.

bob

PatriYacht I pull pressure from same location. Give me 60# of clean, non-fluctuating oil pressure at 215 deg at 6000 and I am good to go.....10# for every 1000 rpm