Originally posted by 1946hamm
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Everyone is an authority on oil. I am not, but I know our flat-tappet engines really depend on zinc as a 'last resort' for engine wear due to lack of lubrication.
Just about any engine oil with '40' (like 10W-40) in the numbers has 1,000ppm of ZDDP (Zinc Dialkyl-Dithio-Phosphate). I use Rotella-T 15W-40 for several reasons. ZDDP content, lubricity, low ash, detergent cleanliness, cost, it beats every API rating, etc.

This oil is NOT recommended for cars with catalytic converters because the platinum substrate can't deal with phosphorus and zinc.
BTW, 'low ash' is a result from burned oil. Remember, piston rings rotate by design. Randomly, the end gaps align causing a blow torch affect down the cylinder which burns oil. Low ash will inhibit sludge which clogs your pickup screen. - Dave
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