7. Aside from the difference in material, the most blatant difference between the blocks are the emulsion holes and the PVCR holes. Though you can’t see it in these behind the power valve, the PVCR holes are significantly lower that the ones in the Holley block. This ensures they do not get uncovered in the turns. When the holes are not submerged in fuel, they can pump air causing a lean spike and a stumble, which in most cases is at the hit of the throttle coming out of a turn.