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Stroked 340 - What Oil to Use?

Engine Issues

  1. KeysCuda

    KeysCuda New Member

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    Last year I bought a 70 Cuda with a stroked 340. The previous owner changed the oil prior to my taking possession. Since it had been a year, I decided that an oil change was in order. I asked the previous owner what he put in the car and he said straight 40W. (zinc additive, of course). Both my husband, who used to build cars, and my current mechanic think that is too heavy and are speculating whether 20W-50 (as recommended by another friend who owns a warehouse full of old Mopars), 10W-30 or something else might be more appropriate.

    We are in South Florida, where the temp is never below 40F and rarely below 60F.

    What do you guys recommend and why? Why is important, so 2 stubborn old car guys can be convinced one way or the other....

    Thank you
     
  2. 340challconvert

    340challconvert Well-Known Member

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    I have heard good things about AMSoil. It has the zinc additive to prevent premature wear in older engines. Highly modified engines will benefit from this type of oil. As far as viscosity, 20w50 should work well in the warmer climate. I used to run it in my 440-6 Challenger in New Jersey in the summer and 10w30 in the winter. JMO
    Check out this review; Do Older Engines Need Oil With ZDDP Additives? – AMSOIL Blog
     
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  3. Cudafever

    Cudafever Well-Known Member

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    20w50 would work good then.
     
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  4. 340challconvert

    340challconvert Well-Known Member

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    Yes. You have a stroker engine, I would think the 20w50 weight oil would help at high engine temps when “enjoying” the engine’s capabilities. Zinc added to oil helps protect metal to metal contact, especially if you are running flat tapped lifters.
     
    Last edited: Aug 13, 2019
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  5. 413

    413 Well-Known Member

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    20/50 is 20 when cold and 50 when hot.

    So that 20/50 oil is thicker than straight 40 weight.

    Oil viscosity depends on bearing clearance and temperature. Do you know the actual bearing clearance?

    Thinner oil cools better.
     
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  6. Cudakiller70

    Cudakiller70 Well-Known Member

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    If I remember right there is a mobil 1 oil that’s good with flat tappet cams. Has a decent amount of zinc also available at Walmart.
     
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  7. Cudakiller70

    Cudakiller70 Well-Known Member

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  8. dolphin3111

    dolphin3111 Member

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    1. Pick the lowest cold viscosity available. 5W or 10W is best. This will provide the best lubrication on cold start up.
    2. Pick the lowest hot viscosity that will give you the hot oil pressure that you want. On an older engine that's in very good shape, 30wt should do it. Otherwise 40wt. On a "loose" race engine, 50wt may be required. Oil pressure requirements are 15psi + 10psi/1000rpm minimum. For all practical purposes, engine oil lubrication ability is independent of viscosity. In an engine the relative speeds of the lubricated parts is so high that lubricant always operates in a "full film" regime. 50wt does not lubricate better than 30wt. In fact in some cases 30 lubricates better. For instance new cars produce very high HP on 0W20 oil without problems.
    3. For a flat tappet engine, pick an oil with 800 to 1200 ppm Zinc equivalent. Beware, too much Zinc in a street engine can cause corrosion over a long period. "Race" oils have way too much Zinc for a street engine. Some have over 2000 ppm. Zinc is not needed in a roller cam engine.
    4. "Full Synthetic" oils are superior in every way to mineral oils. They are made of Polyalphaolefins (PAO) that have a natural affinity for metal on a microscopic level and tend to cling to metal in borderline lube situations. They are pure lubricant with no other hydrocarbons that are found in mineral oil.

    All that having been said Mobil 1 is excellent. Mobil PAO oils are not made from mineral stock, but are polymerized from linear alpha-olefins found in natural gas.
     
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  9. volunteer

    volunteer Member

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    Good post. Hard to dispute (even for us 'non rocket-scientists') - :wtf:
    Recall articles in National Dragster penned by W.J. (the Professor) who explained why he, among a few other P.S. drivers, chose to use a 10w-30 grade over a 20w-50 (or higher).
     
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  10. CITRON YELLA 71

    CITRON YELLA 71 Member

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    I have a 340 stroked to 418 CIA and I have used it from day. I use the Z-Rod 10/30. I believe they have have the best synthetic oil on market. They were the first to market synthetic oil back in 1972. I also use it in my Dodge Ram and my Chrysler 300 SRT 8.
     
  11. Cudafever

    Cudafever Well-Known Member

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    If it is a flat tappet eng Zine is necessary. If they installed a Roller Cam, forget about how much zinc is in there.

    You don't know how much bearing clearance you have so the next best test is oil pressure at idle cold, and idle hot!
    I like to have at least 20 psi at idle(15 + 10 psi per 1000 rpm is a good rule of thumb for oil pressure.)

    This theory is inaccurate because we Also don't know if it is HV pump or standard. but it's the best info without taking the eng apart to find out.

    Now clarity on viscosity aka 10W/30,20W/50 Now the W stand for winter but let just Throw that out the Window and say W stands for Cold Eng and /XX is for a HOT or at running temp on a hot day!
    The oil does NOT get thicker as it get hotter(that's a easy way to think about it but it is Not True)
    Lets just talk straight grades for a second. A straight 20 will have a viscosity of a 20w when cold but it will not, when it is up to temp. it will be thinner. same with a straight 50. A 20w/50 simply means that it has the viscosity of a 20w cold and the viscosity of a hot 50w.
    To throw all that away and make it simpler a 20w will thin out More at running temp then a 20w/50 will. it will still be thinner viscosity when at running temp, just not as much as a straight 20.

    If you only have a light in the dash then buy a aftermarket oil pressure gauge and install it. see what psi you have at idle, cold, and warm. change to a 20W50 and see if this changes. If you are pegging a 80 psi pressure gauge when cold, and have plenty of pressure at warm......a 10w/30 may be a better idea.

    Now that i have said all of that my stroker motor was built for racing, and i us a high volume pump, and live where the heat of the summer is 89 Degrees.
    I run a 5w/20 full synthetic, Peg the oil gauge at idle when cold and have 40 psi at idle when warm. Note: it never start and stays in my garage below 45 degrees.
     
  12. Ridr

    Ridr New Member

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    I run a 416 stroker with roller lifters,rockers and cam. I have been using Amsoil ZRod 10/30 with no loss of oil pressure. I live in AZ and it gets pretty hot here.