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Oil pressure,oil volume question

Discussion in 'The Hokey Ass Message Board' started by Truckedup, Nov 16, 2012.

  1. Truckedup
    Joined: Jul 25, 2006
    Posts: 4,661

    Truckedup
    Member

    When there's a discussion on SBC oil pressure problems,there's always a few replies about the pan being dry because all the oil is up top ,you know the high volume pump controversy.

    But my real question is this,oil pressure and volume and how they relate to each other.
    Suppose you have standard pump in your engine.And when fully warmed up, 50 psi at 3500 rpm.For this discussion,let's say the oil pressure relief valve opens at 50 psi.So the the pump is supplying enough oil pressure to open the relief valve.
    Remove the standard pump and install a high volume pump with not other changes.
    In theory the relief valve will still open at 50 psi
    Question; Is there a relationship between volume and pressure in this example?
    Other words,is the volume of oil limited by the relief valve in this case where both a standard and H/V pump develop the same pressure?
     
  2. Bad Banana
    Joined: Jun 20, 2008
    Posts: 834

    Bad Banana
    Member

    The only way to develop pressure is to completely fill all cavities with oil and then try to pack more into that same cavity. You cannot have low volume and high pressure.

    You are right. The pressure relief dictates the pressure. If your pump is undersized for the volume required to keep the oil cavity full, the pressure will be below the relief pressure. You can however go above the pressure relief if it does not bleed off more than the pump is delivering (i.e. high rpm pumping a high volume of oil with a restricted pressure relief path)

    Is that what you were asking?
     
  3. Actually oil pressure can be your enemy where as volume seldom is a problem. What bad banana says is true you develop pressure by jamming more oil into the passages. That only happens if you have one of two scenarios, a stock pump with blocked or partially blocked passages or a pump that moves a higher volume of oil than the stock pump.

    My Melling will produce over 100 psi with heavy oil in low temp operation. Now this is where you run onto a problem above 110-115 you start washing the babbitt off of the bearings. The solution for my particular situation is to go to winter oil.

    Elevated pressure is a by product of increased volume.

    Here is something to keep in mind, if you are building an engine from scratch and a high volume pump is in the equation there are things that should be done to accomodate the high volume pump. A looser lower end is one thing, I set my engines up loose as a rule because i am going to thrash them for all its worth. A high volume pump is a given from the start. Another thing, especially on a small block chevy, is that you open up the drains a bit. You will still no doubt need to run a higher capacity pan but opening the drains helps keep your topend clear of an over abundance of oil. If you flood your heads or lifter galley it slows your valve train down as well as will eventually seep out of the gaskets.
     
  4. Truckedup
    Joined: Jul 25, 2006
    Posts: 4,661

    Truckedup
    Member

    Ok,I understand you guys.....

    Now let's take this to the H/V controversy and how,in theory, it can drain the oil pan.
    When the oil pressure relief valve in the pump opens,it controls the pressure.Does this also affect oil volume? Other words,does the excess volume also get dumped when the relief valve opens?
     

  5. Bad Banana
    Joined: Jun 20, 2008
    Posts: 834

    Bad Banana
    Member

    An engine's oil system is full of leaks. The oil oozes out of every place it can. Around the edges of bottom end bearings, lifter bores, pushrod ends, ect, and yes, the oil pump pressure relief... Where ever the biggest leaks are the most volume of oil will be. Oil coming out of the pushrod ends and what comes out of lifter "leaks" are about the only way it gets above the camshaft level normally. We are talking 90 degree V8 pushrod engines here that don't have any direct oil pressure in the heads.

    You have 16 squirt guns shooting oil into the valve covers at a pretty good rate at high rpm and the oil only runs back into the pan at a certain speed which is the same at idle as it is at 8000 rpm.

    Now, consider this. You also have G forces when the vehicle is in motion that make oil climb out of the pan. Drag engines have oil climbing the back of the block on hard launch clear up around the distributor in a SBC. That can also put a bunch of oil up into the lifter valley that wasn't really pumped there. Also hard turns right or left can splash oil from the bottom of the pan. Hard braking at the top end of a drag race run can also starve the pan because it will climb up into the timing cover away from the pick up. Couple this with the normal pumping of oil and you soon can starve the pump pick up.

    So... to try to answer your question, the oil pump itself (high volume vs std volume) probably does not have as much to do with pumping the pan dry as much as other internal engine dymanics/clearances and how the engine is being used. People who blame a high volume oil pump for pumping the pan dry are probably not looking at the whole picture.
     
  6. Bad Banana
    Joined: Jun 20, 2008
    Posts: 834

    Bad Banana
    Member

    One other thing I forgot to mention is oil mist. At high rpm, there is more things happeneing much faster and oil gets whipped into the air. This is considerable volume that isn't really being used to get returned and pumped back into the oil passages. There is blow-by happening in the cylinders and that pressure is relieved by vents at the top of the engine (usually valve covers). So this suspended oil gets carried to the top of the engine where it is somewhat calmer and it hopefully settles out of the oil before it goes out of the engine through the venting system. Then it begins it's long slow return to the pan.

    Sorry for the long winded answer but the wife bought some really strong coffee this week and I can't stop typing...LOL :eek:
     
  7. Truckedup
    Joined: Jul 25, 2006
    Posts: 4,661

    Truckedup
    Member

    Ok

    I see that there are a variety of aftermarket oil pump pick ups available. The theory is the stock pick up can cause a "voertex" to form with high oil pump demands. This vortex can cause oil starvation.Perhaps this is what's actually happening and not really a situation where the pan is drained of oil ?
    I have little actual experience here but find all this very interesting....
     
  8. Bad Banana
    Joined: Jun 20, 2008
    Posts: 834

    Bad Banana
    Member

    This is true also. Pick up design is important to how the engine will be used. How it is placed and what size it is makes a difference.
     

  9. Send me an ounce. ;)

    Here is the deal, your bypass may open but on my engine for example if it is making more than 100 PSI the bypass is not bypassing as much as my pump is pumping.

    I originally ran a 4 quart pan in mine (cutting a corner) and it would surge going down the higway at high RPM. Was the pump pumping the pan dry or was it not draining back fast enough? Who knows, I went to a 6 quart pan to solve the problem it was the easiest fix.

    Usage also determins what pan will be used and if it has trap doors or baffles for oil control or not. A crank scraper while its primary function of to keep excess oil off of the counter weights will also return unused oil to the pan.
     
  10. models916
    Joined: Apr 19, 2012
    Posts: 379

    models916
    Member

    If you are pressuring the engine higher than the bypass spring in the pump, your oil is too thick to flow through the bypass orifice back to the pan.
     
  11. CodeMonkey
    Joined: Sep 13, 2012
    Posts: 94

    CodeMonkey
    Member
    from Moline IL

    I seem to remember reading an article back in the 70's about a high speed video that GM shot from inside a crankcase of a running engine - it described how the majority of the oil gathered around the crankshaft, and only when some portion of it reached critical mass did a blob fly off into the crankcase and subsequently back to the oil pan. Granted, it was a stationary engine, so none of the forces of acceleration/deceleration/cornering apply, but it did explain what was happening inside.

    I've done some searching but can't find either the article or the video (assuming it's been digitized). Anybody else remember this??
     
  12. One Finger John
    Joined: Mar 18, 2009
    Posts: 459

    One Finger John
    Member

    In another site (Cadillac), one member, who is using a stock 500 oil pump, oil starved his bottom end and blamed it on the possibility that a "vortex" was to blame. He is running an open round pickup instead of a round pickup that is half or partially covered.

    Will a rectangular pickup break up the vortex effect? And supply a less aerated oil flow?
     
  13. I don't know how to answer your orig. question......however...
    I want to know how much oil goes thru an engine in say.....one minute?

    I suspect the stock oil system puts out way more capacity than the engine ever requires.

    The typical oil system on an engine is a very basic hydraulic system supplying oil for support of the hydrodynamic bearings, and also to carry away heat in the engine.

    Is a higher volume oil pump ever needed?
    Not sure, but sounds like a typical "hot rod". "bigger is better" situation.
    Way back in the day, someone was sitting around wondering about what
    parts could be improved and they decided that the oil pump should be BIGGER and "put out" more oil.

    Question is, why does GM make "high volume" pumps?
    Is there a true need? Is it because they know they can sell them to people that -think- they need them?

    If anything, it sounds like there's more of a need to get the oil away from the crank and back in the pan more efficiently if thats possible.......
    Crank scraper for starters??

    The Grump had a section it the "The small block Chevy racing engine" book, where he basically says they run the stock system in their 600HP
    Pro Stock engines.......because it works very well.
    And they don't need any more volume.
    Running a pump with longer gears requires more HP to turn it .....and puts more oil out the bypass port.

    Hype twists peoples way of thinking in the way of physics and common sense in the racing and hot rodding community.

    Almost every part and system on an engine has at one time or another been "improved" by the racing parts people......weather it needed improving or not....

    dk
     
    Last edited: Nov 16, 2012

  14. Hence the use of summer and winter oil.
     
  15. Bad Banana
    Joined: Jun 20, 2008
    Posts: 834

    Bad Banana
    Member

    Both Beaner and I mentioned it earlier. Production clearances and RPM ranges don't need anything more than a stock volume pump. Once you start to open up oil clearances, the leaks get bigger. Now you can't maintain the 10 psi per 1000 rpm minimum that is a good rule of thumb. Typically, with a stock pump and "racing" type clearances you will have low volume (and by default low pressure) at low rpm (idle speed).

    The pump with larger gears takes a bigger bite of oil as each tooth grabs some as it goes by the inlet. Gives you more volume (pressure) at low speeds. You also need to understand that pumps efficiency goes down as the rpms go up. It isn't pumping at 100% capacity at high rpm. Larger gears help cover that up as well (if you really need the added volume to maintain pressure). The pressure relief helps regulate this. However, if your pressure relief is wide open all the time, your pump is too big. If it hardly or never opens, you are too small.

    It's like anything else. Bigger is not always better and you only need as much pump as the engine requires. Any more than that, you are wasting power and possibly going too far and causing other issues.

    I am no means an expert but I do have quite a bit of real world experience in a lot of different oiling systems. I have hurt my fair share of stuff experimenting but also have found a lot of free power by carefully examining what is really happening when it is running.

    One more tip. Use a good quality gauge and use a large diameter unrestricted line to the gauge. Pay attention to the fitting I.D. and try not to use many elbows. Mearsure pressure close to the bearings as you can. If you are using one of those gauges with an 1/8" line, you might as well have nothing. You engine will be junk way before that guage will tell you anything. You will catch a problem early if you use a good gauge and a large line.
     
  16. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    No one mentioning cavitation...
     
  17. Truckedup
    Joined: Jul 25, 2006
    Posts: 4,661

    Truckedup
    Member

    A stock SBC pump can flow about 7-8 gallons a minute. I believe this is the pump rating and not how much oil actually flows through the engine...
     
  18. BootleggerJim
    Joined: Dec 14, 2007
    Posts: 202

    BootleggerJim
    Member
    from SC

    Oil pressure will never never wash away bearing material, very high oil pressure Will, cause to much oil thrown on the cyl walls and might cause a rear main seal to leak. The point on HV pumps in SBCs is not about pressure or flow. The HV pumps are very much harder to turn and wear out the dist and cam gear, the pump shaft, and mostly the timing set...When I was building race motors, mostly round track stuff, a HV pump would cause a new very good timing set to lose 2 to 4 deg of cam timing in just 2 short races. Not the case with a stock Z28 pump, witch makes more pressure than HV pumps.
     
  19. One Finger John
    Joined: Mar 18, 2009
    Posts: 459

    One Finger John
    Member

    Does "vortex" count?
     
  20. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    no, not the same thing at all.
     
  21. Truckedup
    Joined: Jul 25, 2006
    Posts: 4,661

    Truckedup
    Member

    Come on FalconGeorge,jump right in,I know you have a opinion on this thread.:D
     
  22. I couldn't spell it. ;)
     
  23. Bad Banana
    Joined: Jun 20, 2008
    Posts: 834

    Bad Banana
    Member

    The OP never asked any questions about cavitation. He asked about the difference and/or relationship between pressure and volume. I really do try to stay on topic though I am usually guilty of gliding off... ;)
     
  24. luckyuhaul
    Joined: Jul 11, 2005
    Posts: 182

    luckyuhaul
    Member

    So if you are hitting the by-pass pressure you are wasting energy?

    My experience with a Melling HV pump on a hand built 355 was high blow off pressure when cold , 65 psi.
    Also alot of "sweating" at the gaskets and intake bolts, (even with teflon sealer applied).

    Two modified 307's rebuilt with the stock pump ran about 40 psi max and was so dry externally it looked like it had never been fired up.

    I know the pumps have changed recently, so what is the best set up today?
    I'm leaning towards a stock pump with the heavy duty drive shaft. Good or is there something better? It will be the typical 90% street , 10% strip type of use.

    Getting ready to build another 355 and would like to have the most reliable set-up.
    Oil used is the diesel 15W-40 year round in Florida.
     
  25. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    I do, and some experience as well, but I am keeping my mouth tightly zipped on this one. I'll leave it to the guys who dont see what cavitation has to do with volume/pressure...
     
  26. One Finger John
    Joined: Mar 18, 2009
    Posts: 459

    One Finger John
    Member

    I threw in aerate. Am I good?
     
  27. woodbutcher
    Joined: Apr 25, 2012
    Posts: 3,310

    woodbutcher
    Member

    :D Thanks for this thread.It has answered some questions that I have had about this subject for years.Would painting the inside of the block with a proper paint help with drain back?And what would be a proper way to enlarge the drain back holes in the block? I`m guessing drilling.Thanks.
    Good luck.Have fun.Be safe.
    Leo
     
  28. Your vortex is not a " cavitation"
    But it can cause one by the pump sucking air.

    The scary cause of "cavitation" here is when the pump can not flow to its designed capacity.
    Remember that for later.

    Your high volume pump needs to pump what ? High volume - lots of oil - more than stock.
    So the factory engineers spent oodles of time calculating how much oil Is going to flow thru your engine @ the clearances they have established, the specs. That's the stock flow.
    There are several causes of " cavitations" but the easiest one to cause is restricting the out flow of the pump.
    ( others are inlet restrictions, sucking air, air bubbles stuck in the oil, - couple more that are not applicable to your engine)

    In essence, an engine with stock clearance specs is a restriction on a high volume pump.
    Thats perfect breeding ground for a cavitation & a catastrophic one.

    My two cents on the issue is this:
    If you have low oil pressure on a sloppy worn out engine * get a high volume oil pump and buy some time by increasing the oil flow and raising the pressure.

    If you set your engine up Loose, have done modifications to drastically increase the flow of oil past the bearings * get a HV oil pump.

    If you set your new engine up tight * get a high pressure pump.

    If you set your new engine up to anything or spec published by the manufacturer get a stock pump.
     
  29. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    Cavitation can also occur at the journal/bearing interface as well, independant of any cavitation that occurs in the pump. A little food for thought...
     
  30. The micro bursts, yea another movie.
    I ain't doing it , you do it . If me memtioning 'loose bearings' isn't enough then you'll have to do it.
    The above is for " pump cavitation"
     

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