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Old 11-24-2014, 08:42 AM
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Oil pressure has always; seemed to be open for discussion. If testing a pump, with a gauge in a bath of oil gives you a reading of 65-70 psi, you have to remember that is at the pump. The reading say at the upper oil galley at top of block will be slightly lower. This is going to come from a decrease in volume, which results in lower pressure.
If you speak with a crankshaft manufacturer or one of the engineers, they will still go by the old school method of 10 psi for every 1000 rpm. When you look at the engineering aspect from the bearing manufacturer, the theory changes. The oil and bearing along with the location and design of the crankshafts oil galley, are going to determine the hydrodynamic wedge created between the crank journal and bearing surface. Oil temperature, bearing clearance, and the straightness of the bearing bore ( Main bore straightness in block ) are going to determine how straight the crank rides on bearing. The deflection and rpm of the engine are other factors to consider when setting up bearing clearances along with the viscosity of the oil you will be using.
I have run 54 psi oil pressure in BBC at 6000 rpm, using a Schumann oil pump and having the relief set at 75 psi at the pump incorporating a external .500 relief check ball. That is with 50 wt Redline Synthetic Racing oil, now keep in mind the mains are at .0032, rods at .0026. If I was to tighten the mains up about .0005, that would have a great affect on the oil pressure over all. The oil temp once above 140 will drastically change oil pressure only due to it's flow capabilities, oil must flow and flush the bearing in order to not overheat or scuff the bearing or crank.
Running a high oil pressure not only creates parasitic drag, it excessively loads the distributor gear, cam gear, and shaft housing and bearings in the distributor. High oil pressure also creates spark-scatter, in extreme cases also add the load on the timing chain.
I'm sure all of you know; the oil has to have ample pressure for supplying the mains, rods, cam and lifters, with it's final destination of lubricating the rocker arms and cooling the valve springs. Sucking the oil pan dry and filling the top end of the engine with oil would mean the oil isn't returning fast enough or the oil pan is way too small. Crankshaft windage and pan design are also going to greatly affect oil return and if it is aerated, causing failure of bearings with air pockets mixed in pressurized oil.
So don't be set on having high oil pressure as your safety factor in a build. You could have high pressure and still wipe your bearings out or you could have lower pressure and have like new bearings the next time you freshen up the engine.
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Old 11-24-2014, 09:02 AM
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Originally Posted by MER Performance
Oil pressure has always; seemed to be open for discussion. If testing a pump, with a gauge in a bath of oil gives you a reading of 65-70 psi, you have to remember that is at the pump. The reading say at the upper oil galley at top of block will be slightly lower. This is going to come from a decrease in volume, which results in lower pressure.
If you speak with a crankshaft manufacturer or one of the engineers, they will still go by the old school method of 10 psi for every 1000 rpm. When you look at the engineering aspect from the bearing manufacturer, the theory changes. The oil and bearing along with the location and design of the crankshafts oil galley, are going to determine the hydrodynamic wedge created between the crank journal and bearing surface. Oil temperature, bearing clearance, and the straightness of the bearing bore ( Main bore straightness in block ) are going to determine how straight the crank rides on bearing. The deflection and rpm of the engine are other factors to consider when setting up bearing clearances along with the viscosity of the oil you will be using.
I have run 54 psi oil pressure in BBC at 6000 rpm, using a Schumann oil pump and having the relief set at 75 psi at the pump incorporating a external .500 relief check ball. That is with 50 wt Redline Synthetic Racing oil, now keep in mind the mains are at .0032, rods at .0026. If I was to tighten the mains up about .0005, that would have a great affect on the oil pressure over all. The oil temp once above 140 will drastically change oil pressure only due to it's flow capabilities, oil must flow and flush the bearing in order to not overheat or scuff the bearing or crank.
Running a high oil pressure not only creates parasitic drag, it excessively loads the distributor gear, cam gear, and shaft housing and bearings in the distributor. High oil pressure also creates spark-scatter, in extreme cases also add the load on the timing chain.
I'm sure all of you know; the oil has to have ample pressure for supplying the mains, rods, cam and lifters, with it's final destination of lubricating the rocker arms and cooling the valve springs. Sucking the oil pan dry and filling the top end of the engine with oil would mean the oil isn't returning fast enough or the oil pan is way too small. Crankshaft windage and pan design are also going to greatly affect oil return and if it is aerated, causing failure of bearings with air pockets mixed in pressurized oil.
So don't be set on having high oil pressure as your safety factor in a build. You could have high pressure and still wipe your bearings out or you could have lower pressure and have like new bearings the next time you freshen up the engine.
What would have been the reason I was wiping mains at 55psi and .0030 clearances 1-4 and .0035 on rear main? lack of flow or pressure? this was YEARS ago.... the last build I went 75 psi with shimmed pump and new scat cranks, had GM forged cranks before but wanted new uncut cranks...same clearences, pans, fittings, coolers, and all and just adding pressure I never had an issue again... just curious on thoughts...guys said it was my filters, and the 90 degree stock merc fittings causing my issue, I argued it and proved that was not the issue after 5 years of no issues after changing pump setups.
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Old 11-24-2014, 10:13 AM
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Contamination from dirt, oil temp, or lack of proper flow. Line bore, straightness of mains is critical, without a visual inspection it's hard to say.
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Old 11-24-2014, 10:22 AM
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Originally Posted by MER Performance
Contamination from dirt, oil temp, or lack of proper flow. Line bore, straightness of mains is critical, without a visual inspection it's hard to say.
yea, thats the funny part all of that was addressed, cranks at the end were .020 under so I chitcanned them and got new and then the HV pumps and 75 psi, dunno guess it does not matter now lol was just curious thx bud
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Old 11-24-2014, 03:07 PM
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You guys were right on the money 10778 is what Melling recommended.
After some research and MERs post I`m not sure I really need new ones.. with the spring oilers the pressure is less but the volume may still be there. Seems some guys run fine at 6000 with 50psi for years (in a drag car).
The spring oilers are .040 x 16 = .64. That is over 1/2" of volume loss thou.



Any one recognize what the oil pumps are :







I have 10qt Canton oil pans so I don`t think Id run those dry.. Melling didn`t even ask about oil pans size when they made their recommendation.



Last edited by ICDEDPPL; 11-24-2014 at 03:11 PM.
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Old 11-24-2014, 03:50 PM
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Originally Posted by ICDEDPPL
You guys were right on the money 10778 is what Melling recommended.
After some research and MERs post I`m not sure I really need new ones.. with the spring oilers the pressure is less but the volume may still be there. Seems some guys run fine at 6000 with 50psi for years (in a drag car).
The spring oilers are .040 x 16 = .64. That is over 1/2" of volume loss thou.



Any one recognize what the oil pumps are :







I have 10qt Canton oil pans so I don`t think Id run those dry.. Melling didn`t even ask about oil pans size when they made their recommendation.


you have mark IV blocks? I am looking for a oil pan that clears my engine mounts.... I have very little room between block and mount, the sump needs to start AFTER the mount... but mine are Gen6 ...what mounts do yours have? pic?

[ATTACH=CONFIG]533117[/ATTACH]
Attached Thumbnails Oil pump thread-rod-toss.png  

Last edited by Full Force; 11-24-2014 at 03:57 PM.
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Old 11-24-2014, 03:55 PM
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50 PSI in a boat at 6000 rpm scares me, might be ok, might not.... I think it all depends on the setup, Cliffords 1075's would be 55PSI but also dry sump and all that fun stuff.
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Old 11-24-2014, 03:59 PM
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Iirc, Moroso put those gold tags on their modified melling pumps. I had a pair of the Moroso blueprinted and coated pumps. Didn't keep me from spinning bearings. Some builders just don't watch everything.
Disclaimer* I bought the engines complete with receipts. Line bore was off and clearances on the tight side.
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Old 11-24-2014, 05:05 PM
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Originally Posted by ICDEDPPL
You guys were right on the money 10778 is what Melling recommended.
After some research and MERs post I`m not sure I really need new ones.. with the spring oilers the pressure is less but the volume may still be there. Seems some guys run fine at 6000 with 50psi for years (in a drag car).
The spring oilers are .040 x 16 = .64. That is over 1/2" of volume loss thou.



Any one recognize what the oil pumps are :







I have 10qt Canton oil pans so I don`t think Id run those dry.. Melling didn`t even ask about oil pans size when they made their recommendation.


i spin mine to 6000
+ rpms all the time and less then 50 psi of oil pressure..beeen doing it for over 15 yrs and no issues..a lot of oil pressure robs horse power and puts a major strain on the bronze dist gears.. thats just my o2 and what works for me..
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Old 11-24-2014, 05:16 PM
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Originally Posted by FIXX
i spin mine to 6000
+ rpms all the time and less then 50 psi of oil pressure..beeen doing it for over 15 yrs and no issues..a lot of oil pressure robs horse power and puts a major strain on the bronze dist gears.. thats just my o2 and what works for me..
what main clearence you running?
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