Likely different clearences in the two engines; many of the Cup guys have gone to Honda bearings to reduce friction. Here's a snippet about the bearings themselves Honda Bearing Info
my2c
Jorge
my2c
Jorge
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Lubrizol makes Gibb's. Copy of RL IMO.
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The American Petroleum Institute (API) would classify the base oils used in MicroZol XP1 as Group IV and Group V synthetic base oils.