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Old 10-03-2020, 02:00 PM
avman avman is offline
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Join Date: Nov 2011
Location: New Orleans, La.
Posts: 314
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I have another update on the fan saga. I have the 17" version of the same fan in my Roadrunner, 440 6bbl, modded about the same level as the 421, less the aftermarket rods, and it has flat tappet hydraulic lifters, but a 292°/.509 cam, headers, etc. Vintage Air AC system and Wraptor.
I had NO overheating problem with the Roadrunner, but there are a couple of differences. No goofy Pontiac design water pump divider plate to contend with. The Cold Case radiator is larger. It was programmed by me to run at high speed, where I set it, but I don't think the GTO fan was. I was able to use the "Turn Fan OFF At XX MPH" feature on the Dakota Digital PAC-2800BT electronic fan control module and the temperature on the highway at 70 MPH didn't change with the fan off. Also, my Passon a855 5 speed and 4.10 gears turn the 440 at 2,750 RPM, not 3,500 like the GTO. I already have a TKO600 5 speed for the GTO, but it's not installed yet.
So, AGAIN, I believe the culprit is the divider plate gap being too big, and as long as the flex fan gets the 421GOAT through Cruisin the Coast without overheating, that will suffice. After the week of Cruisin the Coast, I'll take out the fan and radiator, and a good bit of the Wraptor, so I can get the front half of the water pump off and the divider plate, check the gap, and I expect to have to do some massaging to close that gap.
Then I'll try the same setup, and if I find much cooler temps, I'll go back and try the electric fan and shroud assembly again.