I use 2% overbalance in my current 421 turbo combo with an AllPontiac Scat 4.00" crank, and previously also used 2% in my previous high-ish 7000 rpm n/a 400 combo with a factory cast iron crank,for the very reasons Tom detailed above, the bearings always looked good. I settled on re-using the 2% figure for my turbo combo after discussing it with Tom a couple of years ago.
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