0W20 load bearing capability in race block

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Belgian1979

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That's what they said. I interpret it like this : the bypass channel in a typical sbc oil pump enters the inlet channel in a 90° fashion. Due to it being pressurized I think it will hit het opposite wall causing it to go into 2 directions, 1 part in the direction of the pump gears and the other part in the direction of the pickup disturbing the inlet stream. I must say that I witnessed the results from something similar but in a different area. Someone was filling a gasoline tank from a pipe that entered the main fill pipe at an angle of 90°. The flow of the gasoline went in the 2 directions, with one half exiting the open part above the T-fitting, the other half went into the tank below the T-fitting. Schumann indicated that this lowered the inlet pressure, causing cavitation. Of course this could be totally unfounded. I'm not an engineer, so I do not have the necessary capability to verify this. I agree about the possible air entrainment problem, but I have to assume it would be as big with an internal bypass ? Both systems work similar with the one exeption that the external relief valve would exit in the pan below the oil level. I do not see how air could get in there unless the pump was already sucking air.
 
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MolaKule

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Introducing an oil stream into the pan below the oil level would certain reduce air entrainmant. Anytime an oil stream is introduced you have turbulence caused by eddy currents which can increase the potential of air entrainmant. As flow velocity is increased, this potential increases. I am still of the opinion that a 5W20 with your unmodified HV oil pump would be sufficient.
 

Belgian1979

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And would that create enough hydrodynamic wedge to let the oil provide enough oil film strenght ? Anyway, the air entrainment because of injecting the oil will be as worse as in the internaly bypass since it would do it at the same speed and with the same volume. Only the external bypass would allow the air to come out more since it would end up in the sump. with the internal bypass the pump would have to ingest any air that would be caused because of the injection into the inlet, right ?
 
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What 5W-30 oil are you using? Do you have the oil's spec's and PDS info? You have an oil cooler regulated at 175-180F but what is your normal hot sump oil temp'? What is the maximum hot oil temp's when drive hard on the autobahn?
 
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Originally Posted By: Belgian1979
Valvoline 5W30 api sm/cf. No oil temp gauge.
Okay so that is their heavy diesel oil with a HTHSV >3.5cP. You certainly could use something lighter, unfortunately as I mentioned early there isn't a lot of choice in an well additized oil without going with a specialty brand. Valvoline does offer a somewhat lighter oil, their SynPower MXL 0W-30 that's still CF rated; see below: http://www.valvoline-ukraine.com.ua/upload/pdf/Passenger_Car_Motor_Oils_SynPower.pdf I know that there are a lot of lighter C2 rated 0W-30 oils available in Europe you could consider. Many are low and mid SAPS but if you can find one that still as a fairly high ZDDP level that could be a good reasonably priced choice. You should install an oil temp' gauge. I doubt you're seeing oil temp's over 200F even when driven hard. Knowing what your oil temp's are should ease your concern about running a lighter oil which is the original premise of your post.
 

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And would that create enough hydrodynamic wedge to let the oil provide enough oil film [strength] ?
I am convinced it would. You have good oil cooling to moderate the oil temperature. Moderating the oil temperature keeps the viscosity more constant. You have high oil pressure to enhance flow which helps bearing leakage move hot oil to the sump. To place this in perspective, in the late 1950's my father used mineral oil 20W20 API SD to SF oils in his unmodified Buick engines. He changed oil every 3000 miles to 5,000 miles, depending on his mood at the time. He drove his Buicks like a moonshiner. His engines lasted over 150,000 miles. With modern synthetic 5W20 olls as suggested by myself, Falken, Caterham, and others, you should have plenty of anti-wear protection and cleaning capabilities. You seem to be a person who would change his oil using reasonable OCI's. The 100C viscosity difference between a 5W20 and a 5W30 is what, about 1.75 cSt?
 
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Belgian1979

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The oil says it's for both diesel and gasoline engines. As for the difference in cSt at 100°C, on average 2 cSt I think. Someone said to be carefull with the external bypass and air seggregation in the line, which could lead to the air going to the engine and the oil via the bypass. He said the Porsche 928 seemed to suffer from the same problem...Not sure on that. I made an effort to calculate the amount of pressure drop over the internal bypass and it would seem that the bypass hole in the pump towards the inlet would produce a pressure drop of somewhere around 75 psi. I also read that with a pressure drop of 3-4 psi in oil cavitation could occur.
 
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Originally Posted By: Belgian1979
As for the difference in cSt at 100°C, on average 2 cSt I think.
Actually referring to HTHS viscosity (often called bearing viscosity) is more relevant and accurate since that viscosity measure correlates very closely with the oil pressure reading on an OP gauge. For a given VI, the higher the HTHSV rating of an oil the higher the OP you'll register on your gauge. To benefit from the 3.5+cP HTHSV oil you're running now you'd need to be sump oil temps in the 280F range which we know you're not. Running a high VI oil with HTHSV no higher than 3.0-3.1cP will still provide the viscosity reserve you want while reducing the chance of operating in by-pass mode.
Originally Posted By: Belgian1979
He said the Porsche 928 seemed to suffer from the same problem...Not sure on that.
I'm familiar with the lubrication issues with the 928. It wasn't an oil pump issue but oil starvation to a couple bearings. As is often the case, the problem only appeared when racing the 928 and higher than normal rev's were used (over 7,000 rpm). The solution was to machine the crank to allow greater oil flow to the suspect bearings in question (I forget which ones).
 

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I believe that was the no 2 and 6 bearings. I believe they crossdrilled the crank or something like that. The air story seemed strange to me as well. I'm not expert on oils. What oil does have the properties you gave ? PS : the oil I used before was a 10W40 Total 7000 quartz.
 
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I appreciate you're new to the complex subject of motor oil. BTW do you have a flat tappet engine or does it use roller lifters? If it's the latter then any light 0W/5W-30 A1/A5 oil would be fine. The high anti-wear levels that Molekule referred to (ZDDP 1000+ ppm and 200 ppm of moly) would be nice but as I mentioned are hard to find in an off the shelf oil. As he also mentioned (now knowing the car is not actually raced), if you keep your oil change intervals relatively short the lower levels in most oils will be more than adequate.
 

Belgian1979

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Adding to this, I have a feeling I'm running in circles now. I've been asking a lot of people about this but none of the answers are conclusive yet. It seems like everybody is pointing towards another cause in relation to this issue (not aiming at anybody btw). Someone said to me he had the same issue and finally threw the HV pump out and installed a std pump and cured the problem. I have no reason to believe he's not telling the truth. If that's the case I would think it points to the bypass since the only difference between the std pump and the HV is the amount of oilvolume it pumps. In effect std pump would prospone the effect to a higher rpm point but it wouldn't eliminate it. Of course if that rpm point is beyond the rpm capabilities of the engine in question that would not be a problem. On my engine my guess is that a std pump would do the same thing but probably around 6800 or so. I have reason to believe a thinner oil would do basically the same thing. Put the point of pressure drop at a higher rpm point but probably way lower than the rpm capabilities of my engine. At least that the impression changing to the 5W30 gave me. I researched some info about flow of oil and the effect an orifice has. The bypass in these pumps in effect have to pass through an orifice the size of maybe 1/4". The associated pressure drop would be phenominal and basically put pressures at a negative, which is a precursor to cavitation. Since that bypass ends in the inlet, the vapor bubbles would in effect cavitate the pump. Maybe a little simplified as I'm not engineer, but that's the only way I can reason about it.
 
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Just want to be clear on what you're describing. Are you saying your OP is declining at high rev's? In other words, your OP rises with rpm plateaus and then starts to trail off a bit as you approach red line?
 

Belgian1979

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FWIW redline begins at 7500. I'm not sure which situation your describing as the effects were more pronounced with the heavier wt oil. Hot idle oil pressure 25-30, going towards 60 before 5000 and then dropping to 45-50 towards 6000.(10W40 TOTAL) Last time (with the 5W30) hot idle 40-45, rising to 75 psi at around 3000, dropping to 60 psi at 5000 and 55 psi at above 5500. I never went to redline with the pressure dropping off. I stopped at 6000. I have more details with the pressure at 3000 because I kept a very close eye on pressure throughout the revs when I was running the lighter weight. The spring in the bypass is a pink SBC spring and Melling says the bypass is fully open at 70 psi with this spring. Personnally I don't mind running the engine with 60 psi all up to 7500 rpm, but imo it can't be dropping because that basically indicates something is wrong.
 
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So as you say you're oil pump appears to have significant cavitation above 5,000 rpm. While it's not great it still will not prevent you from running a lighter oil. I'd still recommend a light 30wt oil such as Valvoline SynPower ENV C2 5W-30 that was in the link that I provided. You're OP will be lower, but that's a good thing as long as you can maintain 50 psi at 7,500 rpm.
 
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