Oil Pump Info High Volume Myths & Fables Set Straight - Team Camaro Tech
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post #1 of 22 (permalink) Old Apr 12th, 04, 03:10 PM Thread Starter
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This is something that has been discussed many times with people divided on their beiefs. I ran accross this information and thought I would pass it on. #2 seems to be one that is often brought up.


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.

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

2. 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.

3. 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.

4. 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.

5. 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.



Copyright 2003 Melling Engine Parts

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post #2 of 22 (permalink) Old Apr 12th, 04, 03:47 PM
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Mellings in the business of selling oil pumps. Anything they say must be taken with a grain of salt. As for the FE Fords they break oil pump shafts for fun and have such a poor oiling system that it takes 100+ pounds of pressure to get oil to the bearings. Chev. V-8s have an excellent oiling system and if you don't vary too far from stock you have no need of anything near the volume of the high volume pumps.
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post #3 of 22 (permalink) Old Apr 12th, 04, 04:00 PM Thread Starter
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Oger,
I agree Melling sells oil pumps but, they were not pushing their product nor were they saying that everyone should use a high volume. That is why I thought the article was good and informative, it did not read like a sales brochure. Melling also makes/sells standard oil pumps so it doesn't hurt/help them either way.

The point that they make oil pumps, means to me they should know how they work as well as anyone. If not maybe I should be buying a different brand of pump. My understanding is there are only two oil pump manufactures in the US.

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post #4 of 22 (permalink) Old Apr 12th, 04, 07:25 PM
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The thing that I don't get about using a high volume pump is this - unless the oil passages within the block are increased in size, the same amount of oil will reach the bearings at a given pressure regardless of which pump is used, standard or high volume. A higher pressure pump will increase oil flow, but I'm not seeing how the high volume one will. Maybe I'm missing something here?

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post #5 of 22 (permalink) Old Apr 13th, 04, 02:12 AM
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Let me see if I can confuse others.....The oil passages in a SBC engine block(s) are all the same, they are designed to be bigger than the volume the pump can ever pump out. The oil is circulated through the engine via a positive displacement pump. Oil pressure is created by resistance to volume. Max oil pressure is determined by a pressure relief valve at the pump.

If the oil passages are the same size, and the bearing clearances and other restrictions, i.e., lifters, are the same, a standard oil pump will pump X amount of oil at Y pressure. These restrictions, regardless where they are, offer a restriction to flow, the oil passage(s) fill up back to the pump, now the pump 'pumps' more oil into the passage(s), then the relief valve opens up, and bleeds off excess pressure.

The restrictions are smaller volume outlet than the pump volume capability. Thereby, when the galleys are filled, pressure is created.

Example: Start an older engine after sitting for 24 hours. Watch the oil pressure gauge and listen to the engine after it starts. You will hear a knock, whether it be a rod brg, or a lifter leaked down. While watching the oil gauge, you hear the knock go away, then SEE oil pressure on the gauge later. The oil pump has filled the galley void(s). Once its full, the oil pump pumps more oil into it and the restrictions limit the amount of oil bleed-off from the galley.

Now, R&R the oil pump with a high volume pump. All it does is pump more volume of oil due to its longer design as compared to a stock pump. The engine will still make the same pressure, we haven't changed the restriction sizes, thus the same oil pressure is seen on the gauge, or close to it. I'm now shoving more oil into the same space as before, therefore, I'm forcing more oil through the restrictions. Remember? restriction to volume makes pressure. So, now I'm pumping more oil volume, but haven't increased pressure, I haven't changed size of restriction(s).

Now, I decide I want a high pressure oil pump. I replace the relief pressure spring with a, for example, Z/28 spring. I've changed the maximum amount of oil pressure to be created. I haven't increased the restriction(s) size, or the galley volume, so when the high volume pump fills all of this void, its now going to force more oil into this volume. The relief spring is going to allow an increase in oil pressure before it bleeds off extra pressure.

Hopefully, I've explained or totally confused y'all.....

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post #6 of 22 (permalink) Old Apr 13th, 04, 03:56 AM
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Excellent info Royce and Everette [img]graemlins/thumbsup.gif[/img]

I think the debate is really over whether the SBC needs the extra volume -- not on what HVC pumps do or do not do.

Some engines (like the Ford FE, Buick BB, some MOPARs) are clearly into the "need a high volume pump" category. Strange routing or undersized internal passages make it hard for even a high volume pump to supply enough oil to the bearings at higher RPMs on some motors.

The SBC on the other hand IMO does not really NEED a high volume pump when using stock bearing clearances (unless you are supplying oil to a turbo, blower, etc). I think the stock pump with a high pressure spring is adequate for most applications. BUT --- when you start running loose bearing clearances you start "leaking" more oil through each bearing and as a result have less pressure and volume reaching the front bearings. Then its time to step up and increase the supply volume. IMO it is time to step up in an SBC when you start getting over about .0025"

I ran an HV pump in my 383 for the first two years and used HV pumps in other 355s I've built over the years with no problems. Just this last winter I decided to switch to a standard volume blueprinted pump.

So far the only noticeable difference is that the engine has less oil pressure at idle when hot (used to have about 35# now have about 20#). At cruise speeds oil pressure is pretty close to what it was before (now have 40-45 # at 3000 RPM, was a little closer to 45-50# before). At high RPM my oil pressure now goes up to 60# and some change where before it ran up to 80# or even more if it was cold.

My bearing clearances are .002-.0025"

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post #7 of 22 (permalink) Old Apr 13th, 04, 06:10 AM Thread Starter
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Eric,
I agree not every engine "needs" a high volume or high pressure pump. It was just interesting to see all the arguments against them (that we have all heard over and over ie.. pumping the pan dry, spark scatter, oil foaming) be answered by what I would call an "authority".

I have used both high pressure and/or high volume and never had a problem caused by either. It is also not my intent to sell anyone on anything. I ran across what I thought was some good information and when I do, I like to pass it along to people that might be able to learn from it or use it.

I'm just the messenger don't shoot.

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post #8 of 22 (permalink) Old Apr 13th, 04, 10:27 AM
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No - not shooting at you at all . . . it's good info. It just sounded like we were getting ready for the 'ole HV vs. std oil pump debate.

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post #9 of 22 (permalink) Old Apr 13th, 04, 10:42 AM
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Maybe I didn't use the correct wording to state my point. The problem is that the HP- HV pumps also increase the oil pressure so that you do increase the volume of oil in the oil passages. It does cause the bearings to throw more oil on the cylinder walls making the rings work harder and there is an increase in the oil to the upper end which can cause valve guide leakage problems.
People do run them on race only motors ( I did if the motor had alum rods) but a race motor and a street motor are a completely different animal.
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post #10 of 22 (permalink) Old Apr 13th, 04, 01:12 PM Thread Starter
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Eric, I know you weren't shooting. I was directing the first portion of the reply to yours. The rest of it was just in general.

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post #11 of 22 (permalink) Old Apr 13th, 04, 08:31 PM
 
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That info has been posted before in the past. and the same things were said about it. I don' t think we need high volume pumps either. i didnt' run one in my BBC either. Mellings is there to sell oil pumpes, but they do sell stock volume pumps too?? who knows, david vizard doesn't like the high volumes either. who knows
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post #12 of 22 (permalink) Old Apr 14th, 04, 04:24 AM
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Now, R&R the oil pump with a high volume pump. All it does is pump more volume of oil due to its longer design as compared to a stock pump. The engine will still make the same pressure, we haven't changed the restriction sizes, thus the same oil pressure is seen on the gauge, or close to it. I'm now shoving more oil into the same space as before, therefore, I'm forcing more oil through the restrictions. Remember? restriction to volume makes pressure. So, now I'm pumping more oil volume, but haven't increased pressure, I haven't changed size of restriction(s).


Is this the new physics? Same fluid, same pressure, same orifice size but more flow? Roll over, Bernoulli, and tell Navier-Stokes the news...

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post #13 of 22 (permalink) Old Apr 14th, 04, 06:22 AM
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The oil pump relief spring was not removed when the installer welded the new pickup to the cover, hence, the spring lost some of its tension.

Wondered how long it would take somebody to check, Boyles law.......LOL. Goes along with the new math in your kid's school.

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post #14 of 22 (permalink) Old Apr 14th, 04, 05:05 PM
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I agree with onovakind67. You have a pipeline that will flow X. it will still flow the same amount with a larger volume pump. Static pressure is pressure that is not flowing. Residual pressure (the amount you see on your oil pressure gauge) is the pressure left over. The ONLY advantage to a higher volume pump would be if you opened up the restrictions in the engine (clearances in the engine) and the stock pump fails to provide enough volume to build a required residual pressure. A high volume pump installed in a system that is otherwise stock will just cause the relief valve to open further and excess pressure created by the extra volume will just get dumped. The only advantage to installing a high volume pump in a stock engine would be if the engine had worn bearings and low oil pressure problems. Race engines with bigger clearances are another animal. I've seen (i'll call them street performance engines) that have high volume pumps installed and relief springs beefed up and the cam and distributor gears have been destroyed as a result. Restrict the flow of a positive displacement pump and somthings gotta go.
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post #15 of 22 (permalink) Old Apr 15th, 04, 07:09 AM Thread Starter
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GMJim,
I agree and disagree. In your example you are assuming the oil passages are already flowing the maximum with a stock pump. This may or may not be the case, if not then installing a higher flow pump can/will have benefits (if you need the added flow/pressure).

I agree that if you have a tube of a set size and you increase the amount of flow through it (assuming the sane viscosity) the pressure will also increase, once there is enough volume to create pressure.

As we all know our cranks/rods, ride on a cushion of oil (at least we all hope so), so if you have an engine (high compression, high rev'ing, etc...) you will need a cushion that is "firmer" to keep the bearings from being in contact with the crank/rods. To me this means using a higher pressure/volume oil pump will have a firmer cushion (due to more pressure). This is not necessary in all cases but, I can see cases where you would want that.

Without knowing exactly what the maximum flow rate of the oil system/passages is there is really no way to argue for or against (IMO). Since increasing flow has to increase pressure, once you reach the limit you would think the oil pressure gauge would stop at a set amount (since the relief spring/valve would open), once the relief is open then what makes a high pressure/volume pump any different that a standard volume pump? Meaning a standar volume pump "dumps" the oil sooner (at a lower pressure), so if dumping the oil is bad then the standard pump would be worse when it comes to oil "foaming". This is why I also don't believe that the pump causes foaming in either case.

I am not pro or con, for or against high flow oil pumps. I still say you will never pump the pan dry on in a Chevy engine unless you have someting restricting flow back to the pan.

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