[Squidward]

Ok, just watched those vids. What Mike was doing spoke more to equalizing the heat distribution on the heads, front to back. On his first test, what he showed was that providing little to no flow restriction out the back of the head actually made the overall cooling worse.

There are 3 flowpaths in parallel on a Pontiac. One is the internal recirc from the crossover to the timing cover so that there is a small amount of flow with tstat closed. Path number two is out of the tstat to the radiator. Path three is the heater hose. The water pump is capable of "x" amount of flow. Any flow going through the heater hose or the internal recirc is flow that does not go through the radiator. Increasing flow in one parallel path steals from flow in another.

What Mike demonstrated was that porting significant flow out the back of the heads to the timing cover suction port made overall cooling worse because it bypassed the radiator. When flow was restricted, it equalized temps front to back (yay!), but didn't significantly take away from the flow to the radiator. Plumbing the back nipples to the timing cover suction was less desirable, but plumbing the back to the crossover allowed equalization without diverting flow away from the radiator.

IMO, what seems to be the ideal setup would be plumb the back of the heads to the crossover, and if a heater line is desired, tap off the rear crossover, plumb to a heater shut off valve, to the heater core, and then to the timing cover suction.

Also, plumbing directly from the rear head nipple directly to the timing cover suction would be a bad idea, because it diverts flow away from the radiator.

Good stuff, thanks for the discussion.