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Unread 07-15-2011, 02:46 PM   #1606
jkp
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A high volume pump will simply put more of a load on the OPDA gear. Not a good idea.

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Unread 07-15-2011, 04:06 PM   #1607
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Quote:
Originally Posted by GMBNT42 View Post
Hey guys, I got a question, I just recieved my new OEM OPDA today along with a new top end gasket set and just got my head back from the machine shop(decked,cleaned,magnafluxed, new valve installed etc).

Anyway, I put in a new OEM oil pump only about 1k miles ago, but a friend has a new Melling "high volume" oil pump he will sell me for 20 bucks as its not needed for his project. Would it be a good idea to buy and install this oil pump and do you think it would help keep the new OPDA from wearing prematurely? Thoughts?
Quote:
Originally Posted by jkp View Post
A high volume pump will simply put more of a load on the OPDA gear. Not a good idea.
Remember that the OPDA gear also drives the oil pump.

I agree with jkp. We don't need more oil, we need it going to different places (top & bottom bushings of the OPDA).
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Unread 07-16-2011, 05:01 AM   #1608
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Quote:
Originally Posted by jkp View Post
A high volume pump will simply put more of a load on the OPDA gear. Not a good idea.
A high PRESSURE oil pump would put more load on the gears, this I would agree on outright, but a "high volume" oil pump normally means there is only a mild reworking of the oil pumps internal flow design to circulate more oil, this is why its intriging me. Regardless, I just picked it up. 20 bucks seems like a good deal, the pump is definetly built alot better than the factory OEM unit.
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Unread 07-16-2011, 07:38 AM   #1609
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Moving more oil in the same amount of time = more load.

In general, high volume oil pumps are used in racing engines built with loose tolerances. The extra volume is required to keep the oil pressure up due to leakage from the loose tolerances.

A high volume pump will result in higher oil pressure at a given RPM than a standard one up to the point that the pressure relief valve limits the oil pressure.
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Unread 07-16-2011, 07:56 AM   #1610
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Quote:
Originally Posted by jkp View Post
Moving more oil in the same amount of time = more load.

In general, high volume oil pumps are used in racing engines built with loose tolerances. The extra volume is required to keep the oil pressure up due to leakage from the loose tolerances.

A high volume pump will result in higher oil pressure at a given RPM than a standard one up to the point that the pressure relief valve limits the oil pressure.
Not necessarily, the load on the gear is directly related to the resistance of flow. And oil pressure is dictated by the relieve valve/spring in the pump,excess oil will just be recirculated I believe. I know the Melling is advertised to allow 20% more volume over stock, but oil pressure to achieve this won't necessarily be any higher.

I agree high volume/pressure oil pumps make sense for high rpm race applications, does the mild volume increase though of the Melling qualify as a true HV pump or? Turning it by hand the Melling seems to actually have significantly less resistance internally than does the stock OEM pump. A more efficient gear setup could in turn be "tuned" to allow a bit more volume without any more "load" on the cam gear itself?
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Unread 07-16-2011, 08:20 AM   #1611
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Think of it like this: If you are moving 20% more volume, that alone is 20% more weight being pushed by the pump. Moving that extra volume throught the same sized restriction will result in a higher pressure at that RPM compared to the stock volume pump up to the point the relief valve kicks in. For instance, if the stock pump produces 20 PSI at 1000 RPM, the HV pump should produce a higher PSI at the same RPM.

The max load on the OPDA gear at max oil pressure will remain the same as long as the pressure relief valve is not changed. However, most normal driving is not at pressure relief popoff pressure.

Factory Specs:

At Curb Idle Speed* 89.6 kPa (13 psi)

@ 1600 and Higher Rpm 255 - 517 kPa (37 - 75psi)
Oil Pressure Relief 517 kPa (75 psi.)
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Unread 07-16-2011, 08:58 AM   #1612
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Quote:
Originally Posted by jkp View Post
Think of it like this: If you are moving 20% more volume, that alone is 20% more weight being pushed by the pump. Moving that extra volume throught the same sized restriction will result in a higher pressure at that RPM compared to the stock volume pump up to the point the relief valve kicks in. For instance, if the stock pump produces 20 PSI at 1000 RPM, the HV pump should produce a higher PSI at the same RPM.

The max load on the OPDA gear at max oil pressure will remain the same as long as the pressure relief valve is not changed. However, most normal driving is not at pressure relief popoff pressure.

Factory Specs:

At Curb Idle Speed* 89.6 kPa (13 psi)

@ 1600 and Higher Rpm 255 - 517 kPa (37 - 75psi)
Oil Pressure Relief 517 kPa (75 psi.)
Yes I understand that. The question is though, how much more "load" (if any) will the Melling HV pump really put on the OPDA gear by outputting a marginal 20%(via advertising)increase in volume and this is assuming the oil passages are at max capacity before becoming a restriction point, especially at temp? It seems highly insignificant
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Unread 07-16-2011, 09:42 AM   #1613
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I don't remember the fluid flow equations, but at the very least, you're driving more mass along with the volume:


I'll see if I can jog the old memory and come up with the load increase for a 20% increase in flow.

I seem to recall most racers with high volume pumps use a sacrificial bronze distributor drive gear that is replaced frequently.
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Unread 07-16-2011, 10:00 AM   #1614
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Quote:
Originally Posted by jkp
I don't remember the fluid flow equations, but at the very least, you're driving more mass along with the volume:

Video Link: http://www.youtube.com/watch?v=tOiHdIXVWE8

I'll see if I can jog the old memory and come up with the load increase for a 20% increase in flow.

I seem to recall most racers with high volume pumps use a sacrificial bronze distributor drive gear that is replaced frequently.
A increase in volume does not mean that there is a increase in drag necessarily. If the openings on the exit side of the pump are small enough to restrict and raise the pressure, then opening the size of those openings and changing nothing else, would decrease the pressure an increase the volume, at a given rpm, while reducing drag.

I have no idea how the internals of a 4.0 oil pump are made, as I have never opened one up, I'm just making a physical observation.
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Unread 07-16-2011, 10:47 AM   #1615
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The restriction on the oil pump flow is the oil circuit of the engine, not the pump outlet opening.

Volume is contolled by the size of the gears and the amount of oil that they can displace.

The 4.0 pump is simply a geared positive displacement pump.

Guts: http://www.oreillyauto.com/site/c/de...ump+repair+kit
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Unread 07-16-2011, 10:52 AM   #1616
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Quote:
Originally Posted by jkp View Post
The restriction on the oil pump flow is the oil circuit of the engine, not the pump outlet opening.

Volume is contolled by the size of the gears and the amount of oil that they can displace.

The 4.0 pump is simply a geared positive displacement pump.

Guts: http://www.oreillyauto.com/site/c/de...ump+repair+kit
So another question then is the 4.0L engines oil circuit already at max volume flow with the stock pump? Ive seen high volume pumps output significantly more oil without affecting pressure anything significantly.
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Unread 07-16-2011, 11:05 AM   #1617
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I don't know the answer to that one.

The HV pump will limit at 75 PSI if it has the stock limit spring.

At idle, and mid range RPM, I'd think you should see an increse in PSI over stock. You can't trust the dash gauge though. They are skewed to prevent low oil pressure complaints. You'd probably have to hook up a mechanical test gauge to get real meaningful readings.

In fact, the "gauge" in my '06 is nothing more than an idiot light masquerading as a gauge. At something like 4 or 5 PSI, a switch closes telling the computer there is oil pressure, the computer then moves the needle to mid-range and moves it slightly up or down based on engine speed. It reads the same on 15 degree morning start-up or 100 deg day idle in a traffic jam. Useless.

In the '92 you can actually tell if the oil is cold, or up to temp, by the gauge. However, it never dips much below 30 PSI, even with 240,000 mi on it. I'm gussing actual idle pressure is much lower.
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Unread 07-16-2011, 02:14 PM   #1618
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Wow, guys, lively discussion! I have to add a couple of points though. It is not necessarily higher gauge pressure that is in play here. Fluid pressure before an orifice (restriction) is higher than after. So whether there is a restriction before the gauge matters. (Heath’s point) The real pump pressure may be at its outlet or even internally. The only true measure is the torque required to turn both pumps under the same conditions (same engine, same oil, same temp.) at low & high speeds.

A true hi vol pump achieves that added volume in one of two ways, either taller gears (U Tube) or larger (dia.) gears. Some small increase may be achieved through internal improvements. If done internally, the pump may require less torque. So how the Melling achieves higher vol. in the 4.0 pump is the question. I’m not sure you can gain 20% with only internal mods to a dimensionally stock pump. You can compare it to your stock pump. It is probably taller as the Chevy one seen in the video. Also, according to the video, Melling’s hi vol pumps have the hi press spring as well. I don’t think you want that. Whether you can replace it with the spring from your stock pump, I don’t know.

Pushing more oil through the system (up to relief press) will also increase the oil temp I believe.

Another question would be does a stock 4.0 really need or benefit from more flow?

I’ve never dealt with Hesco but they have been around a while & there may be a good reason they add a fitting to spray oil directly onto the cam/OPDA gears on their hi vol pump for the 4.0.

I agree with jkp’s assessments. That said, go ahead GMBNT42, try it. It may not be that much difference. Several guys have inquired about going this route (with a Hesco pump). Keep an eye on OPDA gear wear & keep us posted on your findings.
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Unread 07-16-2011, 02:51 PM   #1619
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Originally Posted by Rubi4MyMrs View Post
Wow, guys, lively discussion! I have to add a couple of points though. It is not necessarily higher gauge pressure that is in play here. Fluid pressure before an orifice (restriction) is higher than after. So whether there is a restriction before the gauge matters. (Heathís point) The real pump pressure may be at its outlet or even internally. The only true measure is the torque required to turn both pumps under the same conditions (same engine, same oil, same temp.) at low & high speeds.

A true hi vol pump achieves that added volume in one of two ways, either taller gears (U Tube) or larger (dia.) gears. Some small increase may be achieved through internal improvements. If done internally, the pump may require less torque. So how the Melling achieves higher vol. in the 4.0 pump is the question. Iím not sure you can gain 20% with only internal mods to a dimensionally stock pump. You can compare it to your stock pump. It is probably taller as the Chevy one seen in the video. Also, according to the video, Mellingís hi vol pumps have the hi press spring as well. I donít think you want that. Whether you can replace it with the spring from your stock pump, I donít know.

Pushing more oil through the system (up to relief press) will also increase the oil temp I believe.

Another question would be does a stock 4.0 really need or benefit from more flow?

Iíve never dealt with Hesco but they have been around a while & there may be a good reason they add a fitting to spray oil directly onto the cam/OPDA gears on their hi vol pump for the 4.0.

I agree with jkpís assessments. That said, go ahead GMBNT42, try it. It may not be that much difference. Several guys have inquired about going this route (with a Hesco pump). Keep an eye on OPDA gear wear & keep us posted on your findings.
The Melling HV oil pump is much bigger than the stock OEM pump in size. Twice as big Id say. Im sure it has a higher pressure rated spring as well too, but under normal driving conditions I feel its rating is in reality irrelevant.

20% volume increase in reality isnt much over stock. Would the 4.0L engine benefit from added flow? Considering the 4.0L is completely cast iron, I dont think added oil volume running through the engine is going to be detrimental other than the question on the OPDA gear. For $20 bucks, its going in.


PS: The Hesco pump is a Melling unit, the only difference is that HESCO charges you twice as much for it. I think HESCO sells it for $160, but the Melling HV pump is only $75 at Autozone retailwise.
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Unread 07-16-2011, 02:57 PM   #1620
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Are you saying that it has the tube to spray oil on the cam gear?
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