Tony D Posted March 27, 2013 Share Posted March 27, 2013 (edited) Pressure is merely a reflection of restriction to FLOW. If you have high flowrates (leakage) from a set volume of pump delivery, you will have low pressure from that variable set. Change any one of the variables, and pressures observed will be changed. Pumps only impart FLOW, pressure is the result of restriction to the imparted flow. This pump is not 'constant displacement' -- it is 'variable linear displacement' as it's flow varies with RPM. It is important to note that LOSSES (flow) can be variable in a different slope depending on RPM. Some engines have things that 'go oval' at higher rpms, and as a result they loose pressure on the top end. Generally it raises linearly with rpm, and the losses remain similarly linear. Do things on the front end (-10 wet sump modification) and your pressure jumps on the back end (oil pressure gauge) with nothing else done because your imparted flow from the pump increase 40% or some ungodly number like that. Same for turbo pump, but it takes horsepower to drive it, and higher than necessary oil pressure costs you horsepower in windage, pump drive losses, hell---you could even spin the timing on a load reversal due to high pump loading! Restrict flow on the suction side, and your pressure observed will be less on the outlet side as the flow is restricted. "I am mainly just trying to make sure there is not any kind of issues that the L28s have with starvation under side loads." "Canton Accusump" For those instantaneous side-load air-sucking, pressure dropping, bearing spinning moments we all get with L-Series...Sounds like you suck the pan of oil, and until it drains back, you suck aerated wind age slung off the crank.Competition pans are 7qts and baffled with trapdoor pickups for just this reason. Edited March 27, 2013 by Tony D Quote Link to comment Share on other sites More sharing options...
djwarner Posted March 27, 2013 Share Posted March 27, 2013 Tony, No disagreements here. "Constant Displacement" is a design term and, of course, volume pumped varies with rpm. What you are describing would occur under two circumstances. One, when under high g turning when oil is sloshed to one side exposing the air to the pickup tube. Baffles are usually added to the sump to minimize this. In this case, oil pressure should return as g loads are reduced. Two, if the oil return to the sump is delayed, the sump can be pumped out. The delay can be caused by a clogged return channel or by poor design when pumped oil volume exceeds the oil returned through the gravity fed channels. Obviously, increasing the pump volume can cause the second condition if a marginal return path isn't also modified. Turbochargers rely on oil flow as a coolant for the bearings and seals. A high volume of oil flow is required because of the high heat of the exhaust side. The small channels inside the turbo and high temperatures make them susceptible to clogging when oil sludges up. I mention this because a company I worked for made the waste gates and control actuators and seals for AirResearch during the 70's and I became intimately aware of the various failure modes. It was common for car companies to under engineer for this higher oil volume requirement. Turbos had their own return lines it was assumed that pressures would not build up. As the turbos sludged up, pressures would increase, causing higher flows to the cylinder heads and more oil retained there. It was critical for owners of these turbo'ed engines observe severe service change oil intervals. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 30, 2013 Author Share Posted March 30, 2013 Shuttlefever, What viscosity oil are you running? Oil pumps are known as a constant displacement pump. That is, for each revolution of the pump, it wants to push out the same number of cc's of oil. This type of pump will generate whatever pressure needed to push out the design volume. What limits the pressure is leakage around the seals and close clearances in the pump body. Pressure continues to build until the various paths for oil flow accept the requisite volume. This is why these pumps come with pressure relief valves. So what determines the pressure required? Size of the oil galleys, clearance of the bearings, viscosity of the oil, temperature that modifies the oil's viscosity, pressure relief valves, and leak paths. The pump is content to generate whatever pressure required to deliver its design volume, even 0 psi. Your last post expresses the concern that the pressure relief valve may be sticking open, however you describe exactly what would happen when the oil thins from rising temperatures. At normal loads oil temperature is near the coolant temperature of 180 degrees. SAE 30 weight oil at 180 degrees is 14 centipoise, SAE 40 measure about 21 centipoise. As you exercise your engine, cylinder blocks, heads, and oil temperatures rise and the oil thins. At 240 degrees, SAE 30 thins to 6 Centipoise and SAE 40 thins to about 8.5 Centipoise. As the Centipoise drops, the resistance to oil flow through the various passages drops and thus the required oil pressure drops. If you pull over and let the engine idle, it will take quite a while to dissipate the heat stored in the engine block, heads, oil, etc. As the engine cools, oil pressure slowly builds. I suggest you get a non contact thermometer from Harbor Freight and watch to see if oil pressure recovery matches the drop in the engine block temperature. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 30, 2013 Author Share Posted March 30, 2013 (edited) Shuttlefever, What viscosity oil are you running? Oil pumps are known as a constant displacement pump. That is, for each revolution of the pump, it wants to push out the same number of cc's of oil. This type of pump will generate whatever pressure needed to push out the design volume. What limits the pressure is leakage around the seals and close clearances in the pump body. Pressure continues to build until the various paths for oil flow accept the requisite volume. This is why these pumps come with pressure relief valves. So what determines the pressure required? Size of the oil galleys, clearance of the bearings, viscosity of the oil, temperature that modifies the oil's viscosity, pressure relief valves, and leak paths. The pump is content to generate whatever pressure required to deliver its design volume, even 0 psi. Your last post expresses the concern that the pressure relief valve may be sticking open, however you describe exactly what would happen when the oil thins from rising temperatures. At normal loads oil temperature is near the coolant temperature of 180 degrees. SAE 30 weight oil at 180 degrees is 14 centipoise, SAE 40 measure about 21 centipoise. As you exercise your engine, cylinder blocks, heads, and oil temperatures rise and the oil thins. At 240 degrees, SAE 30 thins to 6 Centipoise and SAE 40 thins to about 8.5 Centipoise. As the Centipoise drops, the resistance to oil flow through the various passages drops and thus the required oil pressure drops. If you pull over and let the engine idle, it will take quite a while to dissipate the heat stored in the engine block, heads, oil, etc. As the engine cools, oil pressure slowly builds. I suggest you get a non contact thermometer from Harbor Freight and watch to see if oil pressure recovery matches the drop in the engine block ... temperature. I appreciate the engineering stuff but I fear you mis-read the test drive results. I restarted the engine immediately after shutting it off. No cool down time. The engine temp was fairly low as well. I am still pretty convinced its a sticking relief. Plus it gives me an excuse to grab a hi volume pump. If the problem persists after changing the pump, I will see about modifying my pan to incorporate some partitioning in an attempt to get the oil back to the pickup better. My first fear is that the oil is not returning rapidly enough or being kept away from the pickup by centrifugal force in the turns. But after the test flog I am fairly convinced i am having another issue. I may pull the pump this weekend and see if i can see any issues with it. And to answer the viscosity question, I am using 10w40 Mobil 1. Edited March 30, 2013 by shuttlefever Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 30, 2013 Author Share Posted March 30, 2013 I fear there may be a bit of over thinking here. The engine oil pressure kept falling even after the engine went back to idle. In my experience with drag cars, even if the pickup sucks air, your gonna get pressure back when oil gets back to the pan. This just kept falling off slowly. I think if it pulled air it would have lost pressure more rapidly. And if oil was caught somewhere in the engine, an immediate re-start shouldn't have shown normal pressure right away. But maybe i am not thinking hard enough about it... Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 30, 2013 Author Share Posted March 30, 2013 I fear there may be a bit of over thinking here. The engine oil pressure kept falling even after the engine went back to idle. In my experience with drag cars, even if the pickup sucks air, your gonna get pressure back when oil gets back to the pan. This just kept falling off slowly. I think if it pulled air it would have lost pressure more rapidly. And if oil was caught somewhere in the engine, an immediate re-start shouldn't have shown normal pressure right away. But maybe i am not thinking hard enough about it... Quote Link to comment Share on other sites More sharing options...
djwarner Posted March 30, 2013 Share Posted March 30, 2013 Ok, yes, you do seem to have a real problem. If the relief valve is sticking, you would see the pressure drop off you describe. Since you added a second, mechanical gauge, this eliminates the sensor circuit. Since oil starvation is also a potential problem, you might want to consider pulling the oil pan at the same time. Who know what you might find there after 40 years. Sludge might have filled the baffle area or partially blocked your pickup screen. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 30, 2013 Author Share Posted March 30, 2013 Just want to apologize for my multiple posts. My "smart"phone is dumb!!!! Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 31, 2013 Share Posted March 31, 2013 (edited) I fear there may be a bit of over thinking here. The engine oil pressure kept falling even after the engine went back to idle. In my experience with drag cars, even if the pickup sucks air, your gonna get pressure back when oil gets back to the pan. This just kept falling off slowly. I think if it pulled air it would have lost pressure more rapidly. And if oil was caught somewhere in the engine, an immediate re-start shouldn't have shown normal pressure right away. But maybe i am not thinking hard enough about it...On WHAT gauge? It takes FOREVER on the stock electric gauge to recover and read correctly. As stated originally, put a large bore MECHANICAL gauge on there and THEN report. Nothing you are experiencing is ANY different than what has been experienced for 40 years with these cars. Why believe yours is doing something different. If you are pumping oil to the top of the engine, a higher volume pump will make that issue WORSE! Chances are you will pump even your aerated oil up and lose ALL pressure. You won't appreciably improve drain back, your option for pump up (as in any other production engine) is to increase sump volume. It goes "quack", it has webbed feet, it has a bill... Chances are this IS a duck, and not a Caribou. Edited March 31, 2013 by Tony D Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 31, 2013 Author Share Posted March 31, 2013 Ok so first of all, Tony, i put a mechanical guage on it a long time ago, before the test drive that made me believe it was a sticky relief valve. Today I yanked the pump and took it apart to inspect it. The pump itself is fine, a little scarred up but not any worse than I would expect from an older engine. I took the relief valve apart next, and no surprise, it had a sticky point at the open position. I took it apart and polished the bore and piston, and the corners of the ridges. After monkeying with that for a little while I re assembled the pump with a washer behind the spring on the relief valve to bump the relief point. I re-installed the pump on the car and drove it. I flogged around a quarter tank of fuel through it and have not been able to get the pressure to repeat the problem. I won't brag and say I cured the issue but for now I am satisfied with the results. I ran it up over 6 grand several times, in turns and on straights. The pressure never went below 55 psi at high revs. At it's lowest it was around 12 or so at idle. Next autocross is on the 14th. That will be the true test! D~ Quote Link to comment Share on other sites More sharing options...
djwarner Posted March 31, 2013 Share Posted March 31, 2013 Fantastic Shuttlefever! Good to see logic and persistence solving a trouble. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 31, 2013 Share Posted March 31, 2013 Ok so first of all, Tony, i put a mechanical guage on it a long time ago, before the test drive that made me believe it was a sticky relief valve. "Six days ago" -- I missed that in post #16... Last I recalled you "were inclined to put a mechanical gauge on" but missed that second tidbit hidden in there. Should be roughly 10psi per rpm, so that's about right. Quote Link to comment Share on other sites More sharing options...
duragg Posted March 31, 2013 Share Posted March 31, 2013 Mobil VR1 50wt holds up much better for me on full flog mode. But a real oil pan in my future. Oil level, block, pan and dipstick model is a whole nother search thread for the cornering issue. Good job on the PRV fix. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 31, 2013 Author Share Posted March 31, 2013 Well thanks but I am not totally convinced until I run my next autocross. Stay tuned for further reports of impending autocross doom!!! D~ P.S. I am still thinking about a partitioned pan because there may be track days in my future!!! Quote Link to comment Share on other sites More sharing options...
We Bad Posted March 31, 2013 Share Posted March 31, 2013 Just for fun, try this. Get a duplicate oil pan (just like the one under motor), fill it with 5 quarts of water, and hold it in your lap as you ride shotgun in an autocross while someone else drives. See how much water is left in the pan after the run. (Hot engine oil has viscosity approaching that of water and water is much easier to cleanup.) Of course the oil in your engine won't spill out like the water but there is the very real possibility that the pickup will be uncovered briefly and the oil pump will be pumping air bubbles to the bearings. As far as the Accusump goes, it is not a cure all. I've seen road race cars lose bearings because of them. If the oil pick up is uncovered during a long period of braking, like slowing for a turn after a high speed straight, the Accusump will provide the bearings with oil. The problem comes when the driver gets back on the throttle after the turn. The bearings need oil during hard acceleration but part of the oil pump output is then being used to refill the Accusump. It is not a cure all for an improperly baffled pan. Sound advice for autocrossing with a stock oil system: don't start the run a quart low. Quote Link to comment Share on other sites More sharing options...
duragg Posted March 31, 2013 Share Posted March 31, 2013 I like some things about Dave's cast pan: http://www.arizonazcar.com/pan.html I can drive over to his house and pick it up in 15 minutes being #1. I presume it is better than a stock pan. If I call it "Contact Lenses" in my 1040 it would reduce my taxable income for a brief period. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted April 10, 2013 Author Share Posted April 10, 2013 I like some things about Dave's cast pan: http://www.arizonazcar.com/pan.html I can drive over to his house and pick it up in 15 minutes being #1. I presume it is better than a stock pan. If I call it "Contact Lenses" in my 1040 it would reduce my taxable income for a brief period. That pan is DEAD sexy!!! would it work on an s130 car?? It doesn't show it being usable for a zx but it is pretty much the same motor, is there any difference in suspension that would make this pan not work on my 79? Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 11, 2013 Share Posted April 11, 2013 I know the Datsun Comp pan won't fit the S130...without cutting & welding mucho! Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted April 11, 2013 Share Posted April 11, 2013 Steering rack clearance. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted April 11, 2013 Author Share Posted April 11, 2013 Bummer... So, UPDATE!! the weirdness continues. I decided sold some parts and decided that I would go ahead and change the oil pump just because it seemed like a sound thing to do. I opted to stay with the stock volume pump and purchased a new Melling pump. Got the pump stuffed in there, and drove the car. Very happy with the pressure gain the new pump has yielded. However there is still an issue. I can rev the engine all the way up to 5800 rpms and the pressure rises in a nice linear manner. But if i go to 6000 the pressure drops right off and settles at 20. Just like before, only now it at least has better pressure once it stops it's dive. It doesn't matter what gear I am in (first or second). I can immediately shut the engine off and re start it and pressure is normal. The shut off and re start take place over a period of maybe 6 seconds (while coasting). I am still pretty convinced its not starving for oil, but I am fairly stumped on this thing. I shimmed the relief spring just for the heck of it and it does the same. Could there be an issue with the relief valve behind the filter? Any ideas??? Dennis~ Quote Link to comment Share on other sites More sharing options...
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