About 14 years ago, (Fast by) Ferracci came up with the following recommendations by taking a 4V head and turning the cams with an electric motor in the 10,000 rpm region and seeing what happened. He found that these clearances minimized issues with valve bounce and float. These numbers don't have anyting to do with running clearance or heat or anything, they're just what seemed to work the best mechanically.
Intake
Opener - 0.10mm
Closer - 0.10mm
Exhaust
Opener - 0.15mm
Closer - 0.10mm
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