High pressure vs. low pressure oil pump - NCRS Discussion Boards

High pressure vs. low pressure oil pump

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  • Oliver S.
    Very Frequent User
    • December 1, 1999
    • 341

    High pressure vs. low pressure oil pump

    Hello,

    after reading several postings with regard to high pressure vs. low pressure oil pumps I'd like to ask for some clarification:
    My 300hp engine should have a low pressure oil pump. According to the reading I assume a high pressure one was installed after an engine overhaul done under the previous owner. As I read many engine rebuilder do it like this.
    Is there a reason - except PV - to switch back to a low pressure one?

    Regards
    Oliver
  • Duke W.
    Beyond Control Poster
    • January 1, 1993
    • 15672

    #2
    Re: High pressure vs. low pressure oil pump

    Chevrolet built about 20 million Gen I small blocks with standard volume, standard (40-45 psi) pressure oil pumps, and this includes the high revving mechanical lifter engines through late '63. And even then for late '63 through '65 mechanical lifter small blocks got the STANDARD VOLUME pump. The only difference was they got a higher pressure relief spring - 55-60 psi rather than the "standard" 40-45 psi spring.

    TWENTY MILLION ENGINES, and I have never heard of a failure due to lack of sufficient volume or pressure in any road engine, however, that doesn't include failures from oil starvation due to low oil levels while driving the car hard that essentially runs the engine out of oil. But that's not a design issue. That's an "owner is a moron" issue.

    So given this track record, tell my why "bubba the engine builder" insists on a HIGH VOLUME, HIGH PRESSURE pump?

    Anybody?

    If you got one of these damned things and your oil pressure needle is pegged at the upper stop all the time, it will probably not do major harm - just rob some power and fuel economy and raise oil temperature a bit, but anyone who notices the gage while the engine is running will know that bubba rebuilt your enigine!

    In fact, for probably about 90 percent of rebuilds, the OE oil pump is perfectly fine to reuse. Disassemble it (easy), check the gears and housing interior for damage (such as might occur if the pump ingests metal debris), check and correct, if necessary, the end clearance to about .002", and it should be good for at least the next 250K miles. Oil pumps aren't that highly loaded, and being as how they are always full of... OIL, they see very little wear in normal service.

    But "bubba the engine builder" would rather sell you a new high volume, high pressure oil pump (and get the markup on the part) - "because that's what all the racers use" - than spend ten or fifteen minutes inspecting the original.

    And remember that some of the new castings are weaker than OE and have been know to fracture. The OE castings that have been in service for 30 -60 years don't break unless something has disintegrated inside the engine and been ingested by the oil pump or someone hits them dead center with a full blow from a sledge hammer.

    Duke
    Last edited by Duke W.; July 11, 2011, 02:04 PM.

    Comment

    • Ken A.
      Very Frequent User
      • July 31, 1986
      • 929

      #3
      Re: High pressure vs. low pressure oil pump

      I worked at a Chevy dealer in 62 and 63 (the first years of a factory warranty) and saw at least 4 engines that had failed due lack of oil pressure that the Chevy zone rep confirmed as he took a sledgehammer and put a big hole in each block, so us hot rodders couldn't use them!
      You've also got to consider how many of these 40+ year old gauges are reading accurately, especially the 60 pounders that got converted to 80#'s,
      without being recalibrated.

      Comment

      • Michael H.
        Expired
        • January 29, 2008
        • 7477

        #4
        Re: High pressure vs. low pressure oil pump

        Originally posted by Duke Williams (22045)
        If you got one of these damned things and your oil pressure needle is pegged at the upper stop all the time, it will probably not do major harm - just rob some power and fuel economy and raise oil temperature a bit,

        Duke
        ....and wear out the distributor lower bushing and main shaft a lot faster.

        Comment

        • Duke W.
          Beyond Control Poster
          • January 1, 1993
          • 15672

          #5
          Re: High pressure vs. low pressure oil pump

          Engine failure due to "lack of oil pressure" usually means that the engine was run out of oil and the pump sucked air, which yields zero oil pressure. This can seize a bearing and break a rod in a hearbeat at high load and revs.

          It is important to distinguish between poor maintenance on the part of the operator and design issues, and good forensic engineering can usually come up with a probable cause.

          The simple Bourdon tube oil pressure gages used in early Corvettes are very reliable and rarely "drift" in service unless they experience some kind of damage due to poor handling - like dropping it on the ground.

          And keep in mind that these gages are not designed and calibrated for precision readings. They merely give a ballpark reading that's usually accurate to within a few psi of true, but the OE bourdon tube gages are probably more accurate than the later electical gages.

          Gages, whether 60 or 80 psi are already "calibrated" and should read correctly with any pressure up to the end of the scale. The only issue is that if a high pressure pump is used with a 60 psi gage, the gage may be pegged at the high limit most of the time, but that probably won't hurt the gage, and it will still read accurately when pressure is less than 60 psi at low RPM.

          Duke

          Comment

          • Ken A.
            Very Frequent User
            • July 31, 1986
            • 929

            #6
            Re: High pressure vs. low pressure oil pump

            Originally posted by Michael Hanson (4067)
            ....and wear out the distributor lower bushing and main shaft a lot faster.
            That usually takes about 100,000 miles, so I don't think that's an issue.

            Comment

            • Domenic T.
              Expired
              • January 29, 2010
              • 2452

              #7
              Re: High pressure vs. low pressure oil pump

              AMEN to what Duke said.

              I have a pile of good pumps given to me by buba's who replace them.

              I don't think one pump was inspected and am sure buba never saw the inside of the simple pump.

              If you want to beef it up a bit buy the spring or do what we used to do shim the spring with a washer.

              DOM



              Originally posted by Duke Williams (22045)
              Chevrolet built about 20 million Gen I small blocks with standard volume, standard (40-45 psi) pressure oil pumps, and this includes the high revving mechanical lifter engines through late '63. And even then for late '63 through '65 mechanical lifter small blocks got the STANDARD VOLUME pump. The only difference was they got a higher pressure relief spring - 55-60 psi rather than the "standard" 40-45 psi spring.

              TWENTY MILLION ENGINES, and I have never heard of a failure due to lack of sufficient volume or pressure in any road engine, however, that doesn't include failures from oil starvation due to low oil levels while driving the car hard that essentially runs the engine out of oil. But that's not a design issue. That's an "owner is a moron" issue.

              So given this track record, tell my why "bubba the engine builder" insists on a HIGH VOLUME, HIGH PRESSURE pump?

              Anybody?

              If you got one of these damned things and your oil pressure needle is pegged at the upper stop all the time, it will probably not do major harm - just rob some power and fuel economy and raise oil temperature a bit, but anyone who notices the gage while the engine is running will know that bubba rebuilt your enigine!

              In fact, for probably about 90 percent of rebuilds, the OE oil pump is perfectly fine to reuse. Disassemble it (easy), check the gears and housing interior for damage (such as might occur if the pump ingests metal debris), check and correct, if necessary, the end clearance to about .002", and it should be good for at least the next 250K miles. Oil pumps aren't that highly loaded, and being as how they are always full of... OIL, they see very little wear in normal service.

              But "bubba the engine builder" would rather sell you a new high volume, high pressure oil pump (and get the markup on the part) - "because that's what all the racers use" - than spend ten or fifteen minutes inspecting the original.

              And remember that some of the new castings are weaker than OE and have been know to fracture. The OE castings that have been in service for 30 -60 years don't break unless something has disintegrated inside the engine and been ingested by the oil pump or someone hits them dead center with a full blow from a sledge hammer.

              Duke

              Comment

              • Ken A.
                Very Frequent User
                • July 31, 1986
                • 929

                #8
                Re: High pressure vs. low pressure oil pump

                These were NEW cars with less than 12,000 miles driven by regular folks and no they weren't out of oil, or GM would not have warranted them. A 60 # gage rescreened to 80# is NOT correctly calibrated.

                Comment

                • Michael H.
                  Expired
                  • January 29, 2008
                  • 7477

                  #9
                  Re: High pressure vs. low pressure oil pump

                  Originally posted by Ken Anderson (10232)
                  That usually takes about 100,000 miles, so I don't think that's an issue.
                  I've seen a LOT of big block and sp/h perf small block distributor bushings and shafts destroyed with way less than that kind of mileage.

                  A contributing factor was the fact that most owners of solid lifter Corvettes with high pressure pumps at that time used 30W oil instead of 10W30. The oil pump was taking so much HP it would GROAN for the first five minutes of engine operation until the oil thinned a bit as it heated.

                  Comment

                  • Domenic T.
                    Expired
                    • January 29, 2010
                    • 2452

                    #10
                    Re: High pressure vs. low pressure oil pump

                    Originally posted by Ken Anderson (10232)
                    These were NEW cars with less than 12,000 miles driven by regular folks and no they weren't out of oil, or GM would not have warranted them. A 60 # gage rescreened to 80# is NOT correctly calibrated.
                    Ken,

                    My dad was a regular folk along with the other regular folks my other friends had.

                    I almost got the crap beat out of me when my dad found the trophys I won at the strip with his car. It was used but my friends beat the heck out of their folks cars that were new.

                    Funny but the right rear tire ALWAYS wore out before it's time and I actually got good at replacing spider gears, (the good ol days).

                    Also remember that they used break in oil in the early days and that oil didn't lube as good as the regular detergent oil did.

                    DOM

                    Comment

                    • Timothy B.
                      Extremely Frequent Poster
                      • April 30, 1983
                      • 5186

                      #11
                      Re: High pressure vs. low pressure oil pump

                      Ken,

                      If you woorked in a chevy dealership seeing a half dozen small blocks break because of internal problems is probably not bad considering how many went out the door.

                      I agree with others, 45 psi for the small blocks and 60 for the mechanical lifters max..

                      Comment

                      • Domenic T.
                        Expired
                        • January 29, 2010
                        • 2452

                        #12
                        Re: High pressure vs. low pressure oil pump

                        [aaaaaaaaaaaaaaaaa


                        quote=Michael Hanson (4067);564007]I've seen a LOT of big block and sp/h perf small block distributor bushings and shafts destroyed with way less than that kind of mileage.

                        I'll bet the sludge was thick all over from not changing oil and the shaft was hard to remove because of the sludge.

                        When I moved to CA I had a new 65 Impala SS and changed oil every 1,000 miles. When one of my friends heard that he laughed at me and boasted that he NEVER changed oil in his car since new, he only added oil when told to by the gas station attendant.

                        I hate to say it but many treated a car as a disposible item, run it till it quits then get another.

                        American cars that were taken care of PROPERLY lasted a long time, but the sad fact was that most were neglected.

                        I could tell that at tear down.

                        I took the pan off mine with 118K because I ran over a barricade and it looked like day one.

                        Another friend has a Chevy small block with over 400K ( never apart) and only changed the timing chain and fuel pump.

                        DOM



                        A contributing factor was the fact that most owners of solid lifter Corvettes with high pressure pumps at that time used 30W oil instead of 10W30. The oil pump was taking so much HP it would GROAN for the first five minutes of engine operation until the oil thinned a bit as it heated.[/quote]

                        Comment

                        • Duke W.
                          Beyond Control Poster
                          • January 1, 1993
                          • 15672

                          #13
                          Re: High pressure vs. low pressure oil pump

                          Originally posted by Ken Anderson (10232)
                          A 60 # gage rescreened to 80# is NOT correctly calibrated.
                          I'm not aware that this is common practice, but it is clearly "bubba inspired", violates original design, is an improper thing to do (In fact, it is "counterfeit"), and I don't see the point of doing it.

                          As far as the warranty claims are concerned, what evidence led to the conclusion that "low oil pressure", exclusive of oil starvation due to low oil level or excessive dynamic loading that caused oil starvation, was the culprit?

                          If your dealership was indicative of overall failures due to some design problem in the oil system, I'm sure GM would have addressed it, but I am not aware of any significant design changes to the Gen I oil system (exclusive of minor changes such as higher pressure in the late mechanical lifter engines and a change to spin-on oil filters) after 1957.

                          Duke

                          Comment

                          • Ken A.
                            Very Frequent User
                            • July 31, 1986
                            • 929

                            #14
                            Re: High pressure vs. low pressure oil pump

                            Originally posted by Michael Hanson (4067)
                            I've seen a LOT of big block and sp/h perf small block distributor bushings and shafts destroyed with way less than that kind of mileage.

                            A contributing factor was the fact that most owners of solid lifter Corvettes with high pressure pumps at that time used 30W oil instead of 10W30. The oil pump was taking so much HP it would GROAN for the first five minutes of engine operation until the oil thinned a bit as it heated.
                            I've never seen one, but I was always in the South. We used 20-50 Valvoline in our hot rods and I never heard a peep from the oil pumps.
                            These motors regularly saw 7500 RPM & never broke. I had a friend with a 327 that left the line at 10,000 rpm, but not with a stock valve train. The weak link on BOTH big & small blocks were the valve springs and cheapo rocker arms. Stock pump with a shimmed spring was OK but better was the factory Hi-po pumps-they never gave any trouble, unless you broke a valve spring. I guess it's a matter of personal preference as most Corvettes of the C-1 thru C-3 design rarely see a redline. I'm sure the type of oil/oil pump type debate will rage on forever.

                            Comment

                            • Duke W.
                              Beyond Control Poster
                              • January 1, 1993
                              • 15672

                              #15
                              Re: High pressure vs. low pressure oil pump

                              The important thing to remember here - and a lot of guys forget about this - is that most of us want to restore our engines to original factory spec and performance including high revving mechanical lifter engines - maybe with some mild internal improvements like head massaging - and drive them on the road with at most some "light racing", but they are a very tiny minority. Does anyone here do 10,000 RPM clutch drops?

                              Road engines and racing engines (and I mean something like a serious vintage race car not an occasional "weekend warrior") are totally different animals!

                              Unless your requirement is a purpose built-racing engine that will rev considerably beyond the OE redline, leave all the bubba parts like high volume/high pressure oil pumps to bubba and spend your money on worthwhile mods like head massaging and good connecting rods.

                              With the exception of the early connecting rods, small blocks with OE equivalent parts are about as bulletproof as an engine can get. Think back over the years of threads. A lot of problems can be traced to bubba parts like aggressive dynamics cams and gorilla valvesprings that mostly kill low end torque in the rev range where we spend 99 percent of our driving time, notwithstanding the loss of valvetrain durability.

                              Duke

                              Comment

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