Thought I'd better give an update here as ERA Chas was bustin' my balls on another thread for working on the white letters on my new Billboards (but that was last night) instead of solving this problem
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I received the smaller 5" pulley from David Gagnard yesterday afternoon(thank you very much.) With a bit of engineering this morning to resolve the proper backspacing I got it mounted. Fired it up as usual in the driveway and let it warm up. Its warm here, 88*F and 65% humidity, feels like 95F. It would normally get up to 180* operating temp in about 5 minutes (that's with the main puller fan already running from cold start.) I'd say it took a couple minutes longer today, maybe because of the smaller water pump pulley.
I already had my the old 2100 cfm fan (which we thought was a 2700 but wasn't) that had been replaced with the 3600 cfm Zirgo, wired up directly to the 1-wire alternator post and ready to go in the nose. After about 12 minutes the car hit 100C/212*F as usual. I stuck the second fan in the nose against the lower right driver's corner where the radiator exit is and switched it on. The temp almost instantly started dropping and within a minute it settled at 195F. I let it idle for 15 minutes and it never went back up. I switched off the pusher fan and it started climbing. Turned it on and it went right back to 195F.
Also worth noting is that before, I could only see maybe a 5-10 degree differential between the passenger upper corner where the coolant enters versus the driver's lower right where it exits. And a couple inches out from the fan center it would typically be just as hot, 200-210 degrees. With both fans running and engine now at 195F, the differential entry to exit corner is 25 degrees. The core temp right at the exit point is 170F. And the very center of the radiator is only 165F. That is MUCH more in line with what should be happening.
I then added the big honking industrial fan into the mix and the temps dropped another 5-7 degrees. At that point I was getting an 82-85C dash gauge reading and a 180F reading with the IR gun on the manifold where the temp sensor screws in. Icicles started to form so I shut it all down.
Not considering the pulley for a minute, it appears I need more fan or at least a correct shroud to make the fan I have more effective. And I could probably sleep better by going ahead and adding the Fluidyne Cobra 3-row radiator regardless of what else I do.
I have just been informed that I must now go buy some patio furniture to celebrate my discovery, so I am going to let it cool and them put my old water pump pulley back on and try again with the second fan so I can see what impact the smaller pulley had. In the meantime, talk amongst yourselves.