I'm replacing the viscous fan for three reasons:
1) more HP while tracking the car;
2) better airflow while idling either in traffic or at the track waiting for my session;
3) better airflow for air conditioning, esp. since I changed from R12 to R134a.
The Spaal (sp?) fan I'm using is rated at a whopping 2500 CFM. However, I do like the Derale temp. sensor module. I hope I can find it fairly local.