Valvoline VR-1 vs. Lucas Hot Rod oil

I'll reprint the table from the link.
Brad doesn't cite his original source. Possibly speedtalk.
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Some recommended rod bearing oil clearances for various oil viscosities:
.0015 to .0018 for 0W20 or 5W-20
.0020 to .0024 for 5W-30 or 10W30
.0025 to .0029 for 10W-40 or 15W40
.0030 to .0040 for 15W-50 or 20W-50

For main bearings:
.0015 to .0020 for 0W20 or 5W20
.0020 to .0025 for 5W-30 or 10W30
.0026 to .0030 for 10W-40 or 15W40
.0031 to .0041 for 15W-50 or 20W-50

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But it really doesn't have to be multigrades if we're not concerned about cold.
.0015 to .0018 for 20
.002 to .0024 for 30
.0025 to .0029 for 40
.0030 to .004 for 50

For main bearings:
.0015 to .002 for 20
.002 to .0025 for 30
.0026 to .003 for 40
.0031 to .0041 for 50


And for endurance racing of any sort, got to consider there may be difficult at maintaining oil in the pan around 200 * F.
So if running at 230 or 250 or more then a higher viscosity grade will be needed for those events