Turning a 340 crank, How much is to much?

hi, they will run and last at .030 or .040 under.some motors have a smaller dia bearings and run just fine.one of the tricks, was to turn chev crank rod journals to 1.88 which is honda size. smaller dia has less bearing speed therfore less friction =more power. just food for thought.BTW, my stick car is at .020 under, hhmmmm