full groove main bearings oil pressure ?

"I never said anything about " If you increase your radial clearance to try to get more oil flow through" I was talking about cleaning casting flash out of the cast in oil passages! The bearing clearance provides a "calibrated leak" if it is to large you will not have good oil pressure."

Couple things that you might want to research further - first I'm not aware of any "cast in" oil passages. All are drilled so no casting flash. The flash removal is to encourage faster return to the sump because there is significant flashing in the valley, enough in some cases to completely fill what should be cast-in drain back holes. I always deburr the valley and in the past if needed I'll add drainback holes next to the lifter bores and shape/debur them. Second - When we talk about enlarging the passages - we're talking about the passages that go from the right hand lifter galley down to the main bearing bores. There's one for each main saddle, and the ID can vary year to year. I drill all of them to 5/16" mainly because that was the long bit I was able to get my hands on years ago. 9/32s is also popular.