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Old 10-18-2012, 12:54 AM
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Oil Pump

I'm currently rebuilding a 400 small block Chevy. It currently has a high- volume oil pump. Is there a chance a high volume pump will suck the all the oil out of the pan at high rpm? Is it safer to run a standard volume pump? I am running a 6qt. Milodon oil pan.
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Old 10-18-2012, 01:26 AM
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With a 6 qt pan that's a close call. But I'm not experienced enough to accurately answer.how many rpm is expected?

Last edited by birkey; 10-18-2012 at 01:32 AM.
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Old 10-18-2012, 02:05 AM
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High volume oil pumps are really nothing more than band aides for engines with higher bearing tolerences, in other words, give a few thousand more miles of life to a worn out engine that needs a overhaul. The SBC has a excellant oiling system and if your not planning on excessively revving it a standard oil pump works fine. The higher volume pump also robs the engine of about 20 horses over a standard volume pump. I believe the "suck the oil pan dry" to be somewhat of a wives tale, as matter small blocks I've looked at that failed, I never seen one fail from sucking the pan dry. If your worried about oil return there is several places online that show you where to grind the block to speed up oil return greatly such as the small drain back hole beside the distributor hole. The factory usually left this hole small and kinked, some careful work with a air grinder and carbide cutter will clean and open it up good which greatley aides oil drainback and cuts the amount of oil that falls onto the spinning crankshaft so in effect it reduces windage. Also on the block right below where the oil drainback holes are in the heads the block casting has lumps under each one, these can be ground down and smoothed to further speed up oil return. Back in my younger days when I didn't know any better I always used high volume oil pumps because I liked to see the oil pressure gauge stay high, and I never had any issues with it, and that was with the block as it was stock, oil returns not touched. You have to take into consideration you have five quarts of oil in a stock sbc oiling system, and the engine can only take so much oil, regardless of how high the volume of the oil pump is.
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Old 10-18-2012, 04:59 AM
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I have put nearly 1000 Vmiles on my 347. It came with a HV Melling pump and Milodon large capacity sump. The oil pressure has always been around 70-80 psi with the HV pump. I found out from research this pump is overkill for street use, puts extra load on the distributor drive gear as well as the hex pump drive shaft. AS my engine has .0016 clearance on rods and .0017 on the mains , the advice i received after contacting Melling Tech was the standard Ford pump is more than adequate for a 347 street engine.
I did replace the drive pump shaft with an ARP heavy duty unit as i put in a new standard Melling unit.
The information below is from Melling about Chevs which is worth a read.

Courtesy of <a href="http://www.melling.com/techbul1.html" target="_blank">-Melling Engine Parts-</a>


High Volume Pumps, Advantages, Myths & Fables

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.
• It will not wear out distributor gears. The load on the gear is directly related to the resistance to flow. Oil pressure is the measure of resistance to flow. The Ford 427 FE "side oiler" used a pump with relief valve set at 125 psi and it used a standard distributor gear.

Distributor gear failures are usually caused by a worn gear on a new cam gear and/or worn bearings allowing misalignment.
• It will not cause foaming of the oil. With any oil pump, the excess oil not needed by the engine is recirculated within the pump. Any additional foaming is usually created by revving the engine higher. The oil thrown from the rod bearings is going faster and causes the foaming.

This is why high performance engines use a windage tray.
• It will not cause spark scatter. Because of the pump pressure there is a load on the distributor gear. The number of teeth on the oil pump gears determine the number of impulses per revolution of the pump. In a SB Chevy there are seven teeth on each gear giving 14 impulses per revolution. At 6000 RPM the oil pump is turning 3000 RPM or 50 revolutions per second. To have an effect on the distributor, these impulses would have to vibrate the distributor gear through an intermediate shaft that has loose connections at both ends. Spark scatter is usually caused by weak springs in the points or dust inside the distributor cap.

High volume pumps can be a big advantage if used where needed. If installed in an engine that does not need the additional volume, they will not create a problem. The additional flow will be recirculated within the pump.
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Old 10-18-2012, 06:02 AM

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I've not seen a h/v pump suck a pan dry on the street, but have done it at the track..
I've seen more h/v pumps suck the oil pan floor into the oil pump pick up and starve the engine that way..
I have a h/v pump in my 355 but I was told to run the bearing on the loose side when happy gas is part of the power builder..
has this thinking changed.. it was built in the early 90's when I was a young'n.. and still has zero miles on it..
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Old 10-18-2012, 08:57 AM
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When using a low volume oil pump above 4,000 RPM, the filter has 1/2 quart in it, the engine has 2 quarts in it and if the total oil pan capacity is 5 quarts, that leaves 2-1/2 quarts in the oil pan at 4,000 RPM. A standard 20 micron oil filter has 50% reduced flow capacity at 4,000 RPM. In order to maintain a reasonable oil flow to the engine and to prevent the rod bearings from spinning out, the oil by-pass valve begins to open at 4,000 RPM or at 11 PSID (differential) pressure. If you had the bright idea to block the oil by-pass in order to prevent unfiltered oil from entering the engine, ..... the engine goes boom at 5,000 RPM. That is why you need to kick it out of gear and coast in order to allow the engine pick up some oil when you past the finish line.

GM never made a high volume oil pump for regular production engines. However, the GM engineers thought about the possible warranty problems and installed a 21 PSID by-pass valve in the 1993 and later V8 and V6 engines that have remote oil coolers and remote oil filters. GM did not want to buy Melling Select high volume oil pumps and produce an 8 quart oil pan with 2" of ground clearance. What would you say of your wife busted the oil pan puling into the grocery store parking lot?
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Old 10-18-2012, 12:39 PM
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Originally Posted by Oregonite View Post
I'm currently rebuilding a 400 small block Chevy. It currently has a high- volume oil pump. Is there a chance a high volume pump will suck the all the oil out of the pan at high rpm? Is it safer to run a standard volume pump? I am running a 6qt. Milodon oil pan.
NO, this is an old wives tale. Actually high volume and high pressure pumps keep the pump's bypass valve open much, if not all, the time in an engine with OEM production type clearances. So the much of the oil pulled from the sump is actually going around in a circle from the bypass valve back to the intake side of the pump, therefore, very little oil is actually being taken from the sump at any given moment. Assuming there are no drain back issues.

I've been a fairly big proponent of high volume pumps over the years as I do not like the low idle pressures of gear driven pumps, so my habit has been to oversize the pump to drive the idle and low RPM pressure up to cover the number 1 main and rod which is furthest from the pump and last to receive oil. For a high RPM engine (getting above 6000) I have used the high volume pump to cover the centrifugal pumping effect of the rod journals by supplying enough oil that they can't out demand the oil pump. This was is big problem in the days of fully grooved main bearings or grooved main journals. It continues to be a problem with cross drilled crankshafts which a long time ago were often combined with full groove bearing or journals. At least we've learned that grooving creates more problems than it solves. For racing engines that see these extreme RPMs today the better solution is to drop back to the old SBC 2 inch rod journal or custom cranks with the 1.88 inch Honda journal as this lowers the surface velocity between the bearing and journal which in turn lessens the oil supply demand. But this thinking on a high RPM small block Chevy requires a well designed and built 4340 forged or billet crankshaft because the overlap section of the main to rod diameters are substantially reduced which decreases the load transfer area between these journals so the material has to be a lot stronger than that cast or 1000/3140/5000 series steel forgings.

For competition or rock crawler engines that require a wet sump by rules or choice, I still use a high volume pump to overcome the flow losses that come with remote mounted filters and coolers. These engines are, also, usually set up loose so the bottom end bleeds a lot of oil. The purpose here is that much of the cooling of a distance race engine (not that critical on a drag race motor) is through the oil at continuous high power and RPM settings. So I want to pull the heat off the piston underside, insure good piston pin and camshaft lubrication and get the heat out of the bearing and journal interfaces. To do that I just move more oil through the lubrication, filtering, and cooling circuit. On top of that I'm concerned about dropped throttle, maneuvering, gear changes, and returning to up throttle conditions so I again want an idle oil pressure floor of about 40 pounds to insure that the distant number 1 main has a ready, uninterrupted oil supply. These engines also get an Accu-Sump installed which is an accumulator that reserves oil against a spring loaded diaphragm/piston that will be injected if the system pressure falls to less than the spring's. I need to also point out that in such engine configurations I also modify the pump by-pass such that the return to the intake side of the pump is plugged and the vented oil is sprayed back into the pan through a screen to absorb some of its kinetic energy. So the bypass oil isn’t just heated and rerouted into the intake oil stream.

The big issue that can result from a high volume pump is a lot of windage whipping around with the crankshaft. To keep from overcoming the oil rings, reduce windage drag on the crank assembly, and put more oil into the pan so it has more time to rest and de-aerate before going back into the pump, a crank scraper and good windage tray as well as traps around the pickup and rear baffle become important. The trap doors and baffle (these keep the oil around the pickup and from climbing the read of the sump then getting into the spinning rear counterweight) are extremely important on all forms of wet sump race and rock crawler engines. The scraper which can be a simple strip of metal on the right (passenger) side of the upper pan to pan rail or a conformal shape that fastens at the pan rail catches the oil being flung upwards from crank rotation and directs it back under the windage tray into the sump. The windage tray needs many louvers that face into the direction the crank is coming from. They face left (driver’s side) to catch the oil being flung downward to separate it from the windage and direct it into the sump.
I very much like the Milodon pans that use the full length windage tray, but the 4/5ths tray and the diamond screen tray are acceptable alternatives.

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Old 10-18-2012, 03:50 PM
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That is the best explanation I have read about using a high volume or a standard volume oil pump.

To further expand on the subject, if your engine is not equipped with a factory remote oil filter, a standard volume oil pump may be all that is required. Be advised, most production engine re-builders have a policy to set up rod and main bearing clearances on the wide side of standard without their customers knowing it because they do not know how the engine will be used. That helps avoid come-backs due to spun rod bearings.

Rod side clearances and bearing clearances are normally set up wider if the engine will see high RPM and with that in mind, the camshaft grind should determine if you will need a high volume oil pump. Meaning, if you install a radical camshaft, you are expecting some high RPM...right? If that is the case, a high volume oil pump should be considered and a Melling Select 10552 10% higher volume oil pump fills the bill. Be advised, Melling Select high volume oil pumps are NOT bolt in pumps. They require a special oil pump pick up assembly that is 1/2" shorter than stock or an oil pan that is 1/2" deeper than stock.

I used a Melling Select 10552 oil pump because my daily driver engine is set up .010" wider rod side clearances and .003" wider rod and main bearing clearances because my engine will occasionally see 5,700 RPM bursts of speed. It is also equipped with a factory remote oil filter with eight feet of plumbing. I replaced the original equipment 11 PSID oil by-pass in the block with a 21 PSID by-pass in order to better regulate unfiltered oil from entering the engine. The OE remote oil filter adapter by-pass remained 11 PSID. That oil by-pass is only in case of excessive oil filter restriction but that implies neglect by the car owner.

Last edited by MouseFink; 10-18-2012 at 03:57 PM.
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