Icanfixall, I remember reading that you did this on the first heads, do you know how much you enlarged the hole? Also, did you change the shape of it any? I understand what your saying about not all the air flows through it, but I'd say about 80-90% of it since there is no combustion chaimber in the head and the pistons do stick up out of the block some. I guess what I was getting at is when the piston comes up, where does all the air go?
Through that hole into the precup.
From my research I found that the turbo 6.5 GM's have a larger and different shape hole into the precup. Since the 7.3 was never really designed for a turbo, all the cups were the same, so my thought is, why did GM change the design with the addition of a turbo?