Many of my hot rods I've owned for 40 years with flat tappet cams I've run Valvoline 10-40 and never an issue. My Fiat Spider, I ran Rotella diesel 15-40 oil, as that is what the Fiat guys push. My Pontiac I started with 10-40 Brad Penn and then switched to Driven 10-40, since that is what my engine builder suggested. I asked why the Driven oil stays so clean looking compared to my Valvoline? He said the Valvoline type oils keep contaminants suspended in oil, while Drive oil, the contaminants lay in the bottom of oil pan. I learn new things on oil here and other places I had no idea about. I'm no engineer.
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