Ask Away! with Jeff Smith: Does My Mild Small Block Chevy Need a High Pressure or High Volume Oil Pump?

 (Image/Jim Smart)

I am about to rebuild a 350 small block Chevy that originally came out of a truck. We’re going to add new forged pistons, better rods, and if I can wrangle up the cash perhaps a nice set of aluminum heads. Here’s my question. With all these good parts I was going to add a stock oil pump since I don’t plan to race this engine or anything but a friend said I should use a high volume, high pressure pump to protect the bearings. I never really considered that before. Does my engine need that? 


Let’s start with a fact or two and then you can decide.

First, there have been literally millions of small block Chevy engines built and driven hundreds of millions of miles using a stock volume and pressure oil pump. I think that sometimes car guys just look for a reason to add a high performance part to their engine. In your case, it sounds as if a high volume, high pressure pump is really unnecessary.

However having said that, there is certainly nothing wrong with adding a high volume pump to your engine if it makes you feel better.

You mentioned that you’re trying to save money for a set of really good heads. Good cylinder heads are an excellent way to help make more power. A high volume pump will not help make power but may in fact hurt the power. Remember that if you are moving more oil at higher pressure, that energy has to come from somewhere and that amount of energy required (as small as it may be) will be subtracted from flywheel horsepower. It’s that simple.

Another way to look at this is that a stock small block Chevy oil pump is designed to be able to push sufficient oil against all the restrictions in the engine in order to supply oil throughout the engine with more than sufficient pressure. So now, if you add a pump with greater volume potential this means the pump has to work harder to push oil into the engine because it’s moving a greater volume of oil. So common sense would dictate that this is expending additional work toward an objective that isn’t necessary.

Now, if you build the engine with much larger clearances, then that’s a different story. A normal 350 small block Chevy’s main journal bearing clearance is right around 0.0025 inch. If the clearance is closer to 0.0030 inch, then that additional space will allow more oil to flow and should probably be accompanied by the use of both thicker viscosity oil and a high volume oil pump.

There are no real advantages to increasing clearances. In fact, NASCAR small blocks run at very tight clearances to reduce the amount of windage (oil leaking out of the bearings) that will hurt horsepower at higher engine speeds. So it’s actually to your advantage to keep the clearances in the middle (around 0.0020 to 0.0025 inch) to reduce the amount of oil escaping the bearings.

A long time ago, Steve Brule’ and I did a oil pump test at Westech where we ran a stock volume pump, a high volume, then a high volume/high pressure pump, followed by a big block Chevy pump. Not surprisingly, as the volume and pressure demands went up with bigger pumps, the power suffered and the stock pump made the most overall power. What was surprising was how well the big block Chevy pump performed. We theorized that the greater number of teeth on the big block pump improved its performance compared to the fewer number of teeth on the high volume small block pump.

Speaking of gear designs, Melling offers a complete redesigned oil pump gear set they call the Shark Tooth.

The original small block Chevy oil pump design uses straight spur cut gears that tend to exhibit excessive leakage past the gears that contribute to pressure fluctuations that load the distributor gear drive unevenly. The Melling Shark Tooth design reshapes the gears into an asymmetrical helical shape that evens out the pressure fluctuations and reduces leakage past the gears. The Shark Tooth pump is quite a bit more expensive than the standard small block pump but for a high-tech, high rpm small block it might be a great addition.

A closely related point to your question is the viscosity of the oil that you will be running. The move in modern cars is to thinner viscosity oils now like a 5w30 or even a 5w20. When running a standard bearing clearance like the above-mentioned 0.0025 inch for the small block Chevy, it’s best to run a 10w30 or 10w40 oil in order to create the proper lubrication barrier between the bearings and the crank journal. Thinner oils can be used if you go with tighter clearances. Generally, thinner oils will allow the engine to make a slight amount of power increase due to reduced pumping losses but these are one to two horsepower gains at most. Conversely, you can see a one or two horsepower drop by running a 20w50 instead of a 10w30.

So the bottom line for a mild 350 small block or any mild street engine is that you don’t need a high volume or high pressure pump to do an adequate job. Think more about perhaps a windage tray and better oil as a way to help your engine manage the lubrication task.

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  1. Tyrone E Gross (aka) Tystyx says:

    I love these type of questions. I’ve been building Engines for over 45 years,,,stock & high performance,{GM/Ford/Mopar}
    And if it’s Stock, I would install a Stock Oil Pump.
    Anything High Performance,a High Volume Pump. (I don’t believe in High Pressure Pumps) My belief is with any engine 50psi oil pressure on starting up(cold engine)is plenty,30-40 hot idling engine,,, perfect.
    I’m Old School Taught. I’m not crazy on Synthetic Oils,as a matter of fact I do honestly think it’s a total waste of money,unless you’re in Deep Space,or at the Bottom of the Ocean, it’s a total waste of money. [FYI::much of recycled/reclaimed oil is a semi synthetic oil,a centrifuge can not separate conventionl oil from synthetic oil]
    Good Luck!

  2. High pressure oil pumps put unnecessarily more load on the distributor gear.

  3. John Riparetti says:

    What about if I’m running a solid cam with restrictors

  4. Awesome information! I learn a lot from these type questions!

  5. Rod Sabatoni says:

    Great advice! Thanks

  6. and a hi volume pump will find ways to piss out oil that you never though of …like out the dipstick tube pcv valves etc.

  7. David Bryant says:

    Good to know.

  8. And why forged Pistons in basically a stock rebuild admittedly not for performance? Better to save it in heads, hypereutectic pistons are fine.

    FWIW, Melling actually told me that it would be a good idea to run their high pressure/high volume small block pump (the one derived from the big block pump) in an application for low RPM usage where the engine tends to be lugged. Oil pressure drop is the same, but from 50 to 20psi is a lot better than 30 to 5.

  9. Hello, have a question please. I have a fresly rebuilt 355. 60 pounds oil pressure but at high rpm my oil pressure drops. What can it be? Foaming? Im i emptying the oil pan (stock melling pump) ?

    Thank you in advance. René

    • Ad an extra quart of oil and see what the pressure is at high rpm or buy some pushrods with restricters in them to keep more oil in bottom end

    • Jeff+Smith says:

      I’d start by adding a 1/2 quart and see what happens. If the pressure improves, then it’s draining the oil pan. More than likely however, that the oil pan has too much oil in the pan and it’s foaming under high rpm and causing the pressure to drop. Drain a 1/2 quart and check the pressure at high rpm. Keep draining 1/2 quart until the pressure stays constant. Then drain all the oil and measure the amount in the pan. That’s how much the engine needs. People often think more oil is better – but often it results in the problem you are experiencing.

  10. Gary LaChance says:

    Great information, a very good breakdown of comparison between all available, great yes thank you

  11. James Trangmar says:

    What about a boat. The high volume

  12. Watch Engine Masters season 6 episode 93, the oil pump, pump off. It was very interesting it might help to answer your question and just might surprise you.

  13. What determines pressure is volume and resistance. If your running tight clearance no need for high volume pump. If your running loose,which I don’t know if anybody does anymore, you may need a high volume pump. In other words,if you have a loose setup or a worn engine you may need higher volume to make up for what “leaks” around main,rod and cam bearings. High volume and tight clearance = oil being pumped into top of engine quicker than in drains back to sump

    • Robert Berger says:

      Volume & pressure are two different things from the oil pump.
      Volume is determined by the length of the two gears in the pump housing. HI Vol are 25% longer gears.

      Pressure is determined by which spring is installed in the pump. There are dozens of choices and are colored coded for identification.

  14. What about .oo13-.0018 on clearance on 383 stroker trying to get some thin oil to run tight clearance

  15. Jeff polsene says:

    I agree with the pressures you suggest. I do not agree with the synthetic oil is a waste of time. I run Mobil1, and I live in az. The heat here is quite hot. Standard 10 w 40 runs out of a drain plug like water. I used to live in wi. In cold weather oil just dont flow. Synthetic takes care of both problems, and is 400% more slippery than conventional oil.My brother switched to synthetic in his suburban. He noticed shortly after, he had to lower his idle about 300 rpm. That’s how much synthetic freed up his engine, just by being more slippery. So say what you will, but it’s been proven synthetic oil is superior to conventional oil in every way.

  16. I have bought oil pumps that came with a second pressure relief spring with a higher spring tension when a higher pressure is needed. Making it a “high-pressure” pump. When the pump is supplying more oil than the overall system can flow, some of the oil goes back into the sump at whatever pressure it takes to compress the spring. Higher pressure within the pump means more heat goes into the oil.

  17. Denise M. Wright says:

    My 99 vortec 5.7 never had more than 20 lbs cold less than 10 hot idle and around 10 at 210 degrees water temp and 4500 RPM. Eventually spun a rod bearing and destroyed the crank. Rebuilt I insisted on a HV pump now never less than 40lbs no matter how hard I load it and no more valvetrain rattle and piston slap at cold idle. And no more of my backside chewing holes in the seat waiting for the bearing knock to happen. Yes I’ve lost a distributor gear but they are intentionally sacrificial that’s why they’re brass. Better that than another GD crank.

  18. Bill balbach says:

    About dist gear got a shock when my extremely expensive hi po eng man put a composite gear in with my very expensive 496 strocker bbc,but they work perfect.he also drills holes in dist for extra oiling.bill balbach

  19. So what’s the price difference between a high volume and a stock pump? You are buying a new pump, right? You aren’t saving money using the old pump are you? You can save even more money using used bearings, those used lifter will be okay on that new cam, that ridge isn’t that big, use the old pistons and rings.
    BTW the high volume pump just dumps the excess back into the inlet tube so it uses no more energy and doesn’t dump it in the pan and foam the oil or anything. I was also taught you need 10psi per 1000 revs, so at 7000 you need 70psi which isn’t stock pressure of 45 to 50.

  20. Ignoring the fact that you can tailor clearances and add restrictors to limit top end oiling, etc., on any given engine with a given viscosity oil, the only way to raise oil pressure is to force more volume through the oil circuit. If you add a high volume pump with larger gears the pressure must increase… otherwise you are just bypass all the extra volume, which needlessly adds heat. Conversely, if you shim the stock pump bypass spring and pressure increases, more volume is being forced through the oil circuit rather than the bypass. If increasing bypass spring pressure does not increase oil pressure, a higher volume pump may be needed.

    • Robert Berger says:

      To simulate your statement, think of a garden hose.
      The cheap ones are only 1/2 dia. The high quality are 3/4″ dia.
      If you turn on the faucet full blast with the smaller hose, you will have pressure but not much volume.
      With the larger hose opened only half way, you will have lots of volume with low pressure.
      Just like the bigger gears in a HV pump and larger oil pick-up tube diameter, more volume but std press.
      Pump options:
      std vol / std press
      std vol / HI press
      HI vol / std press
      HI vol / HI press

  21. Larry Crawford says:

    What is that red grease that is coming out of the plastic bottle onto the “oil pump gears” in the illustration of the oil pump. Does it help prime the pump and does it desolve in the engine oil or does it contaminated the engine oil.

    • Hey Larry, thanks for reading and great question. That is engine assembly lube, and the image is from another article about building up a Chevy 307 small block penned by OnAllCylinders contributor Jim Smart. Here’s the relevant part of the article to your question:

      “Oil pumps should never be installed right out of the box, though a lot of builders do that. Jeff checks tolerances and the oil pressure relief valve for proper function, then fills the pump cavity with engine assembly lube for a good wet start-up.”

      You can read the whole story on that 307 here.

  22. I used a BB pump on a 355 back in 76 when I was a wee 18 year old, if it got more than 1 1/2 qts low on oil it would suck the pan dry when I jumped on it.

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