I think a lot of engine builders recommend thick oil because it works. Hard to beat experience. I know one career SS racer that tried using thin oil and he had a rod knocking the following race. It may have had nothing to do with the weight of the oil. But if one races for twenty five years using thick oil and never has a bearing failure, then tries light oil and has a problem.... He's going to be hesitant to run thin oil. Butler's used to recommend straight straight 50.
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