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Old 09-16-2012, 06:41 PM
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sbc Looses oil pressure under hard load

Hello,
I have a sbc that evan after the rebuild under hard load WOT will start to drop oil pressure
The bearings all clearanced out at 1.5 thou
it has never blown up and i built it when i was 15 now i am 35
I pound the crap out of it but i freshen it up every couple years and the bearings are mint everytime
HV/HP melling oilpump
hyd 480 cam
cold 65-70 psi
cruise speed 2200rpm @45-50psi
under wot it will drop down to 30ish you let off and slowly comes back up
thanks

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Old 09-16-2012, 07:10 PM
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Lose the HV/HP pump and you will more than likely not have the drop off. No need for that pump, probably starting to run your pan dry at WOT.....
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Old 09-16-2012, 09:14 PM
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Quote:
Originally Posted by Steel View Post
Lose the HV/HP pump and you will more than likely not have the drop off. No need for that pump, probably starting to run your pan dry at WOT.....
right on have you used a stock pick up on this oil pump?I did and thought maybe it could be an issue too.
So i thought about it pumping the oil up top and sucking air but as hard as i ran it i figured if it was that then i should have seen the bearings beat up on the freshen...Or I thought it would have spit its guts out all over the place
thanks
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Old 09-16-2012, 10:43 PM
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Put an extra quart of oil in it to test for it sucking dry. Maybe it's just your gauge.
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Old 09-16-2012, 10:55 PM
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well i tried that too and no change.I thought for sure that it would puke if it was no oil. I pushed it harder and it still hasnt skipped a beat.
When i checked the bearings the last time i mean they were like new
Heard rumors about the Fram filters from walmart so i am going to try a new Wix
thanks
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Old 09-17-2012, 12:09 AM
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sbc Looses oil pressure under hard load

What kind of oil pan are you using with the HV/HP oil pump? You should be using a 7-8 qt. oil pan.
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Old 09-17-2012, 01:03 AM
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stock no baffel
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Old 09-17-2012, 01:26 AM
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oil

first, is it a manual gauge or elec.
you should try another gauge. any shop will have a quick screw on one to compare.

You can have air in the line too.

I have seen engines pump too much oil to top but they were liters or push rod issues.

The HV pump doing it is a myth.
True HV put more drag on cam and are unnecessary but this is NOT the cause of your problem.

with valve cover off you can make a splash guard and start it for 15 seconds. If it had the right amount up there it will drip and make a little mess , but if it is getting to much, it will be all over fast, you will know it, it will be a real mess fast.



Push in pump screens can be loose or suck air because there are hard to put on even by a pro, chevys worst design, even tack welded they can still suck air but if you really suck enough air your lifters will start to make noise.
I suspect the screen is loose.
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Old 09-17-2012, 01:36 AM
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thanks
screen isnt loose we just had it down and it is spot welded.
the gauge shouldnt be the issue as the motor was previously in a different car.
Lifters were just replaced with the cam{no issues just got one smig bigger
Hyd cam
stock pushrods
stock rockers
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Old 09-17-2012, 07:31 AM
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Its sucking air.
The design of some screens can cause air to be entrained into the oil when the oil flow demand gets very high.
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Old 09-17-2012, 04:24 PM
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Quote:
Originally Posted by Ruthlessmr View Post
right on have you used a stock pick up on this oil pump?I did and thought maybe it could be an issue too.
So i thought about it pumping the oil up top and sucking air but as hard as i ran it i figured if it was that then i should have seen the bearings beat up on the freshen...Or I thought it would have spit its guts out all over the place
thanks

You won't see any damage to your bearings unless you're losing all pressure, which from your description you are not.

Sounds like cavitation to me. I don't know what your turning the engine to, but I still believe if you lose the HV/HP pump your system will not be so prone to cavitation at high RPM, thus allowing your oil pressure to remain constant....
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Old 09-17-2012, 06:16 PM
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You could be whipping that oil up too, causing that cavitation. Switch that HV pump out for a Melling Select series pump. Standard volume, use the high pressure spring it comes with.
The Fram filter is not the problem.
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Old 09-18-2012, 12:17 AM
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oil pump

Sorry guys but the pump is not the problem if there is one.
There is only so much oil that can get through lifters , push rods, etc.
Lets just say for fun it could, so it pumps so much oil to the oil to the top of the engine and the huge drain back holes did not return the oil fast enough, where is that oil?
Oh and if an engine were whipping up oil to make enough air mixed in oil the lifters would make noise and
it would get frothy, milky color. More likely it is the screen installed wrong.
Easy? Well it would be on top of the heads, under the valve cover.
It would not matter what type seals one has, there would be so much oil it would burn oil, smoke, get oil in PVC. Remember it has to "suck" half the oil out to get below the screen, that is if it is 1/2 inch from the bottom of the pan.
I dont care if he is doing a wheelie its not going to happen if all is assembled right. Any pump can be high pressure with springs. A stock pump can make enough pressure to blow the filter off easy.
Volume? Like I said, if it is built right there is only so much volume that can be pumped though a lifter and .060" push rod.
I have had defective lifters from comp that flooded the top with oil and caused other issues but even that did not make pressure drop.
Thats all I have to say about that

I could be wrong, I was once, but call melling and ask them you will see.
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Old 09-18-2012, 06:44 AM
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When you "put bearings in " did you replace the cam bearings ? That would be my concern.
dave
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Old 09-18-2012, 09:55 AM
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thanks guys
the pick up is 3/8 inch above pan
spot welded
cam bearings were replaced the 2nd time down and its been down 4 times for bearings rings and a cam swap
about the only thing never changed was the oil pump,pick up ,pan,
i pulled the oilpump down everytime and it still looks good
the pick up is stock so i was thinking maybe to small of holes on the screen it seems to look like the screen is sucked in
I am going to try a different pump and pick up
thanks
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