There has been discussion in the Pontiac world that tying the two rear water passages together would offer better and equalized cooling to the rear of the heads. I have seen guys that have went to much greater trouble than I did to try to accomplish this. Personally, after having done this and giving it more thinking, I don't think it helps any at all and it a total waste of time. I believe the original Pontiac engineers knew exactly what they were doing and how best to do it. ALL that rear water port is for is to circulate a very small portion of heated water to the heating coil. The cooling system will work best (I believe) either as produced or with the rear port plugged. I was having cooling problems at one time and my temps did not change with or without my setup. I have yet to see anyone prove this actually does any good. So bottom line, just leave it like the factory did it.