Oil pressure question

[Guest zfan]

I just brought my car home from the shop it just got the 383 with 4340 crank, 6" H beam rods and JE pistons installed. I am running a high volume oil pump and was suprised to find that when running for 30 minutes when I let it idle at 850 rpms at a light I am only at 18 lbs of oil pressure when I drive along at 2500 rpms I get 50 lbs of pressure.

 

This just seems to low or am I being peranoid. You must understand my last 2 383's died from spun rod bearings on one due to a dropped pick up tube and the other due to a cracked crankshaft and several spun bearings.

 

I am running 10/30 oil and the engine had maybe 30 miles or 45 minutes of run time before I drove it home 20 miles.

 

Mike

[grumpyvette]

zfan

to answer your question, thats normal with 10w30 oil and normal clearances and NO you should NOT use a thicker viscosity, and yes SYNTHETIC is REALLY BETTER, keep in mind PRESURE is the way we measure the resistance to flow,NOT how much oil flows, or how well its luberacating, worry if and only if the pressure drops below 15 psi at idle or it fails to jump significantly as soon as the rpms build slightly, by the time you get to 3000rpm you should see 45 psi minimum and by 5500rpm 60 psi plus

 

 

heres an old post on oil systems it answers most questions

 

 

 

the short answer is its always better to use a HV pump with BOTH a WINDAGE SCREEN AND A HIGH VOLUUM BAFFLED OIL PAN....AS those three components are necessary to get the whole lubracation SYSTEM working together as its designed to BUT sucking the pan dry of oil with a HV oil pump is about 90% a myth in a chevy V8, (I say 90% because it MIGHT be possiable if all your return drain passages were partly blocked and you were running a 5 qt oil pan with no baffles, under some conditions like very hard accelleration or braking where much of the oil was forced to one end of the oil pan by G-forces but generally its damn hard to get even a 5 quart oil pan in a chevy to suck air into the oil pan pick-up, and its quite difficult to get the oil pump pick-up uncovered simply because theres just no where for 5 quarts of oil to go, that it won,t drain back quickly in a well maintained engine.

years ago I saw an in depth article about this that SMOKEY YUNICK did useing a plexiglass window in the oil pan and valve covers, even at 7000rpm a high voluum oil pump coild not get most of the oil into the upper engine, the valve covers never got full like some folfs will tell you and the oil pan always had more than enought oil flow returningg to keep the oil pump pick-up well covered.

 

read this over carefully

IVE POSTED MOST OF THIS BEFORE BUT IT FITS HERE AS A SOURCE OF INFO FOR THE NEWER GUYS

http://www.melling.com/highvol.html

http://www.melling.com/engoil.html

 

ok lets look at a few things, pressure is the result of a resistance to flow , no matter how much oil is put out by the oil pump there is almost no pressure unless there is a resistance to that oil flow and the main resistance is from oil trying to flow through the bearing surface clearances and once the pumps output pressure exceeds the engines ability to accept the oilflow at the max pressure the oil return system/bypass spring allows the oil circles back through the pump ,now the amount of oil flow necessary to reach the furthest parts in the engine from the oil pump does not go up in direct relation to rpm, but it instead increases with rpm at a steadly increaseing rate that increases faster than the engine rpm due to centrifugal force draining the oil from the rods as they swing faster and faster since energy increases with the square of the velocity the rate of oil use goes up quite a bit faster due to the greatly increased (G-FORCES) pulling oil from the rod bearings over 5000rpm going to 8000rpm than the rate of oil flow increases from 2000 rpm to 5000rpm (the same 3000rpm spread) and remember the often stated (10 lbs per 1000rpm)needs to be measured at the furthest rod and main bearing from the pump not at the pump itself, next lets look at the oil flow itself, you have about 5-6 quarts in an average small block now the valve covers never get and hold more than about 1/3 to 2/3 of a quart each even at 8000 rpm (high speed photography by SMOKEY YUNICK doing stock car engine research with clear plastic valve covers prove that from what Ive read) theres about 1 quart in the lifter gallery at max and theres about 1 quart in the filter and in the oil passages in the block, that leaves at least 2 quarts in the pan at all times and for those that want to tell me about oil wrapped around the crankshaft at high rpms try squirting oil on a spinning surface doing even 2000rpm (yes thats right its thrown off as fast as it hits by centrifugal force, yes its possiable for the crankshaft WITHOUT A WINDAGE SCREEN to keep acting like a propeler and pulling oil around with it in the crank case but thats what the wrap around style milodon type windage screen is designed to stop)the only way to run out of oil is to start with less than 4 quarts or to plug the oil return passages in the lifter gallery with sludge or gasket material! now add a good windage tray and a crank scrapper and almost all the oil is returned to the sump as it enters the area of the spinning crankshaft! forming a more or less endless supply to the oil pump, BTW almost all pro teams now use DRY SUMP SYSTEMS WITH POSITIVE DISPLACEMENT GERATOR PUMPS that are 3,4,or 5 stage pumps each section of which has more voluum than a standard voluum oil pump because its been found total oil control is necessary at high rpms to keep bearings cool and lubed

 

NOW I POSTED THIS BEFORE BUT IT NEEDs REPEATING

ok look at it this way,what your trying to do here is keep an pressureized oil film on the surface of all the bearings to lube and cool them and have enough oil spraying from the rod and main bearing clearances to lube the cam and cylinder walls/rings. now a standard pump does a good job up to 5000rpm and 400 hp but above 6000rpm and 400hp the bearings are under more stress and need more oilflow to cool and because the pressure on the bearings is greater you need higher pressures to maintain that oilfilm.lets look at the flow verus pressure curve. [color:"red"] since oil is a liquid its non-compressable and flow will increase with rpm up to the point where the bypass circuit starts to re-route the excess flow at the point were the pressure exceeds the bypass spring pressure. but the voluum will be equal to the pumps sweep voluum times the rpm of the pump, since the high voluum pump has a sweep voluum 1.3-1.5 times the standard pump voluum it will push 1.3-1.5 times the voluum of oil up to the bypass cicuit cut in point,that means that since the engine bearings leakage rate increases faster as the rpms increase because the clearances don,t change but the bleed off rate does that the amount of oil and the pressure that it is under will increase faster and reach the bypass circuit pressure faster with the high voluum pump. the advantage here is that the metal parts MUST be floated on that oil film to keep the metal parts from touching/wearing and the more leakage points the oil flows by the less the voluum of oil thats available for each leakage point beyond it and as the oil heats up it becomes easier to push through the clearences.now as the rpms and cylinder preasures increase in your goal to add power the loads trying to squeeze that oil out of those clearances also increase. ALL mods that increase power either increase rpms,cylinder preasures or reduce friction or mechanical losses. there are many oil leakage points(100) in a standard chevy engine.

16 lifter to push rod points

16 pushrod to rocker arm points

32 lifter bores 16 x 2 ends

10 main bearing edges

9 cam bearing edges

16 rod bearing edges

2 distributor shaft leaks

1 distributor shaft to shim above the cam gear(some engines [/color] that have an oil pressure feed distributor shaft bearing.)

so the more oil voluum the better,(AS LONG AS ITS TOTALLY UNDER CONTROL ON BOTH THE PRESSURE AND RETURN/SCAVAGEING SIDES OF THE SYSTEMchevy did an excelent job in the design but as the stresses increase the cooling voluum of the extra oil available from the larger pump helps to prevent lubracation delivery failure, do you need a better pump below 5000rpm or 400hp (no) above that level the extra oil will definitely help possiable deficient oil flow and bearing cooling and a simple increase in pressure does not provide a big increase in voluum that may be necessary to keep that oil film in the correct places at the correct voluum at all times.the stock system was designed for a 265cid engine in a passenger car turning a max of about 6000 rpm but only haveing the stress of under 300hp transmitted to the bearings, Im sure the orriginal designers never thought that the sbc or bbc would someday be asked to on occasion hold up to 450-800hp and 6000-8000 rpm.nore did they forsee valvesprings that placed 500lbs and up loads on the lifters and the use of over 9 to 1 compression ratios in the original design so the oil voluums and pressures necessary to cool those valve springs and bearings at those stress levels were never taken into account for that either.

 

Continued (oil Pan/pump)

the oil pump can only pump as much oil as the engine clearances allow at the max pressure that the oil pump bye -pass circuit will allow, and no more. for your idea to be correct (which it could be under some conditions)the oil flow through the engine clearances would need to be so great that the pump turning at 3500rpm,7000rpm engine speed(remember the pump spins 1/2 the speed the crank does)and most likely pumping at max pressure could lower the oil level to the point that the pick-up becomes uncovered or a vortex as you call it forms and the pump starts sucking air.

 

 

now under hard acceleration it is very possiable for the pickup on ANY oil pump to to become uncovered in a oil pan that has less than 5qt capacity and with no oil control baffles as the oil rushes to the rear of the oil pan if the pick-up is located in mid pan or under hard brakeing if the pick-up is located at the rear of the pan on a non- oil baffle controlled pan.

 

I will grant you that it is possiable for ANY oil pump to pump a good amount of oil into the lifter gallery at high rpms IF THE OIL RETURN PASSAGES IN THE HEADS AND LIFTER GALLERY ARE BLOCKED, preventing its normal return to the crankcase

 

, but running a high volume oil pump will have little or nothing to do with how much oil is in the pan if the engines drain back holes are clear and your useing a milodon style windage screen. I have several times had that same complaint about lack of oil pressure under acceleration but it is caused by a non-baffled pan or the pickup mounted so close to the pan bottom that the pump cant get a good intake flow, if you carefully check youll find that on a dyno runs it seldom happens,because the oil is constantly removed by the windage screen is returned to the sump, most of the oil pumped into the system exits at the rod and main bearing clearances or at the cam bearings and from the lifter bores lower ends, its not the constant oil flow or lack of oil into the rocker arms that has the big effect on total oil flow as SMOKEY YUNICKS PHOTOGRAPIC RESEARCH PROVED YEARS AGO,its the oil flowing from the bearings and lifters and that oil flow is quickly returned to the sump by a windage screen scrapeing it off the spinning crank and rods as the spinning assembly passes over the windage screen. in effect most of the oil in an engine works like your timeing chain in that it constantly cycles top to botton and back never getting higher than the cam bearing lifter area.

 

now what does quite frequently happen is that the guys installing a high volume oil pump just swap out the standard pump, reinstall the stock or simular pick-up and bolt on the pan with the pick-up in the stock possition on the oil pump. the stock pick-up is mounted about 3/8" off the pan bottom,the high volume pump is normally equiped with impeller gears about .3 inches longer than stock, the high volume pump body is that much lower in the pan, resultting in the pick-up being only about 1/8" from the pan bottom. the result is that on a normal chevy oil pump pick-up this leave a space of about 1/8" x 2.5" for oil to flow into the pump. at low rpms this works but as the rpms climb the pick-up that can,t get any oil to pump cavitates as it spins and fails to pump oil, result oil pressure drops untill rpms are lowered no matter how much oil is over the pick-up. simply checking to make sure that anout 1/2" of space is under the pick-up when the pan is installed cures that problem (a simple trick is to weld a 1/2" thick nut to the oil pump Pick-up base and test fitting the pan BEFORE WELDING THE PICK-UP TO THE PUMP BODY)]

 

what it comes down too in every case that Ive looked into so far is a improperly positioned pick-up or a non- baffled oil pan without a windage screen or less than 5 qts of oil in the system, not a problem of all available oil being pumped into the lifter gallery and valve covers like some people would like you to think.

 

the MELLING COMPANY HAS THIS TO SAY

 

Most of the stock automobile engines are designed to operate from idle to 4500 RPM. The original volume and pressure oil pump will work fine in this type of application. As the demands on the engine increase so does the demands on the oiling system and pump.

The oil pump's most difficult task is to supply oil to the connecting rod bearing that is the farthest from the pump. To reach this bearing, the oil travels from three to four feet, turns numerous square corners thru small holes in the crankshaft to the rod bearing. The rod bearing doesn't help matters. It is traveling in a circle which means centrifugal force is pulling the oil out of the bearing.

 

A 350 Chevy has a 3.4811 stroke and a 2.111 rod journal. The outer edge of the journal travels 17.5311 every revolution. At 1000 RPM, the outer edge is traveling at 16.6 MPH and 74.7 MPH at 4500 RPM. If we take this engine to 6500 the outer edge is up to 107.9 and at 8500 it is 141.1 MPH. Now imagine driving a car around a curve at those speeds and you can feel the centrifugal force. Now imagine doing it around a circle with a 5.581, diameter.

 

The size of the gears or rotors determines the amount of oil a pump can move at any given RPM. Resistance to this movement creates the pressure. If a pump is not large enough to meet the demands of the engine, there will not be any pressure. Or if the demands of the engine are increased beyond the pumps capabilities there will be a loss of oil pressure. This is where high volume pumps come in; they take care of any increased demands of the engine.

 

Increases in the engine's oil requirements come from higher RPM, being able to rev faster, increased bearing clearances, remote oil cooler and/or filter and any combination of these. Most high volume pumps also have a increase in pressure to help get the oil out to the bearings faster.

 

That is what a high volume pump will do. Now let Is consider what it will not do.

 

It will not replace a rebuild in a worn-out engine. It may increase pressure but the engine is still worn-out.

 

It will not pump the oil pan dry. Both solid and hydraulic lifters have metering valves to limit flow of the oil to the top of the engine. If a pan is pumped dry, it is because the holes that drain oil back to the pan are plugged. If the high volume pump is also higher pressure, there will be a slight increase in flow to the top.

 

let me point out this chart

 

 

http://www.diabolicalperformance.com/clearances.html

heres other info,

http://www.babcox.com/editorial/ar/ar10180.htm

 

http://www.thirskauto.net/BearingPics.html

 

http://www.waynesgarage.com/docs/oil.htm

 

http://www.jimcookperformance.com/TechNotes/TN%2023.html

 

 

 

 

http://www.cryoeng.com/images/EngineDurabilitySecrets.htm

 

http://www.melling.com/engoil.html

 

http://members.aol.com/carleyware/library/engine2t.htm the oil pump can only pump as much oil as the engine clearances allow at the max pressure that the oil pump bye -pass circuit will allow, and no more. for your idea to be correct (which it could be under some conditions)the oil flow through the engine clearances would need to be so great that the pump turning at 3500rpm,7000rpm engine speed(remember the pump spins 1/2 the speed the crank does)and most likely pumping at max pressure could lower the oil level to the point that the pick-up becomes uncovered or a vortex as you call it forms and the pump starts sucking air.

 

 

now under hard acceleration it is very possiable for the pickup on ANY oil pump to to become uncovered in a oil pan that has less than 5qt capacity and with no oil control baffles as the oil rushes to the rear of the oil pan if the pick-up is located in mid pan or under hard brakeing if the pick-up is located at the rear of the pan on a non- oil baffle controlled pan.

 

I will grant you that it is possiable for ANY oil pump to pump a good amount of oil into the lifter gallery at high rpms IF THE OIL RETURN PASSAGES IN THE HEADS AND LIFTER GALLERY ARE BLOCKED, preventing its normal return to the crankcase

 

, but running a high volume oil pump will have little or nothing to do with how much oil is in the pan if the engines drain back holes are clear and ESPECIALLY if your useing a milodon style windage screen.

look closely youll notice most oil never gets pumped higher than the lifters before returning to the oil pan sump,

I have several times had that same complaint about lack of oil pressure under acceleration but it is caused by a non-baffled pan or the pickup mounted so close to the pan bottom that the pump cant get a good intake flow, if you carefully check youll find that on a dyno runs it seldom happens,because the oil is constantly removed by the windage screen is returned to the sump, most of the oil pumped into the system exits at the rod and main bearing clearances or at the cam bearings and from the lifter bores lower ends, its not the constant oil flow or lack of oil into the rocker arms that has the big effect on total oil flow as SMOKEY YUNICKS PHOTOGRAPIC RESEARCH PROVED YEARS AGO,its the oil flowing from the bearings and lifters and that oil flow is quickly returned to the sump by a windage screen scrapeing it off the spinning crank and rods as the spinning assembly passes over the windage screen. in effect most of the oil in an engine works like your timeing chain in that it constantly cycles top to botton and back never getting higher than the cam bearing lifter area.

 

"I don't need to do anything to the HV oil pump except put it in there right? "

 

YES and NO! you still NEED to check that the oil pump pick-up is mounted so its 3/8"-1/2" from the oil pan floor surface ( DON,T GUESS CHECK!!)a lump of modeling clay can be used to check clearance by putting a lump on the lower pick-up surface and placing the oil pan on the block as a quick test fit using only the corner 4 bolts and the gasket without any sealant.

then after making 100% sure it fits with the correct clearance you need to silver solder or weld or braze the oil pump pick up to the pump AFTER temp removing the bye pass circuit spring to prevent it getting anealled OR you can use a BOLT ON pick-up with red loctite

 

your local arts/craft store sells it in 1 lb blocks I usually use brite blue or black but suit your self, a digital caliper or even a ruler will get you the thickness measurement your looking for)

 

http://store.yahoo.com/teacher-parent-store/modelingclay.html

 

http://www.guildcraftinc.com/ProductInfo.aspx?productid=102-500

 

once its correctly possitioned ,remove the bye pass spring and gears from the oil pump,and have the pick-up BRAZED or welded to the pump body, then after it cools (DON,T DROP IT IN WATER LET IT AIR COOL)replace the byepass spring and gears, lube the pump, check clearances and install! just be damn sure its BRAZED or welded in the correct location as that 3/8"-1/2" is critical to good oil voluum feeding the pick-up

 

btw check that the pick-up tube entering the pump is not extending into the pump body too far and binding the pump gears, Ive seen that happen (rarely but its comon enought that ive seen it a few times)

and check that the gears rotate smoothly (i usually oil the gears with a mall amount of assembly lube mixed with oil before assembling the pump)and its best to use a oil pump drive with a steel collar not plastic

[280zwitha383]

Wow........

[Guest zfan]

Grumpy,

 

Thanks alot for all the info. I appreciate that.

 

Mike