I am sure I will get a lot of grief but…
I use straight 30 or 40 without any zinc. The ZINC thing is in my opinion is much ado about nothing. Years ago, I talked with someone who does the testing of engine oils for a very large organization. Their job is to evaluate the oil companies’ oil for conformance to their published specifications. They have a room of engines that are the most blueprinted and checked engines in the world. They must be to detect what oil does or does not due to them. They are also all non-hydraulic cam engines.
They have found no wear differences with or without zinc in the engines. Period.
They have found that a number of camshafts in the 1990's, when a LOT of cam production moved out of the USA, had issues with Rockwell Hardness on the lobes. In fact, I know of several engine builders that now send out camshafts and lifters for Rockwell testing. Guess what? Several of them fail even recently.
I suspect that proper hardness treating of cams and lifters drives much of the speculation about Zinc. I could not find one single "hard science" document on the subject. A lot of opinion, but nothing definitive where two exactly the same engines in all respects were run with and without zinc and the wear differences were measured and documented..
My 1947 Desoto Suburban engine I built 20 years ago, has about 75K miles on it. I run it in the Hills of San Francisco and the Interstate to my place out of town at 70 MPH. The car is about 5000 pounds. I looked at the cam a while back with the side covers off and a bore scope. The cam was NOS when it went in. It looks fine with no evidence of advanced wear. I never used any zinc.
James.
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