Between 1400 to 1700 on your chassis.
The higher the resistor, the higher the cut-in..but still lower than stock

I like to stay on the upper end to save fan draw and wear, but some guys go as low as 1100 ..NOT my recommend for your car/chassis..V8 cars use the lower cut-in b/c they run hotter. If you are running under 100C , you do not need a high fan . But waiting til 107 is a bit much, so anywhere close to 100C cut-in will give you adequate airflow when needed and a cut-off about 95/96. That is perfect for 104 HFM/SFI system.

Buy different ones and experiment.
And be aware that as you lower the cut-in , you are also lowering the cut-out..so you want to watch both when choosing.- these fans are not continuous run rated. They are AUX only , and should be used as such.

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A Dalton