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
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
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.
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.
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.
Found it. Look at bottom line of page 3 15w50. If it’s good enough for flat tappet I’m sure it’s good for most everything else. Additives like zinc sometimes fight with oil additives already in most oils. So just adding zinc may or may not be good. https://mobiloil.com/~/media/amer/us/pvl/files/pdfs/mobil-1-oil-product-specs-guide.pdf
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.
