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The hole in the crank only needs to match the leak rate of the rod/journal. Larger won't benefit uness your running large clearances.
It seems the bottom line is to overcome the centripetal forces added to the oil inside the crank as it spins. Cross drilling does that as does the pressure trickery the 993 does (from what I understand it's no cross drilled).
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1967 912 with centerlocks… 10 years and still in pieces!
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