Actually the way it works is that the flow is roughly half from either end versus a standard block, so the velocity is lower in the back of the main gallery, where there have been ideas/reports that the higher velocity makes it easier for the oil to 'shoot by' main #4. But the pressures don't 'cancel'; the pressures would be high on each and lower in the middle, and higher in the middle than with the stock feed, and the average pressure is higher throughout (assuming the split and plumbing to each end is good). The stock setup has pressures dropping from back to front, with the center and front pressures being lower than with the dual feed, because the full flow has to pass through the back half of the gallery.
