Hot Rod magazine had an article about fans a few years ago. The clear winner was electric because of no parasitic loss. As for mechanical the best was Flex-a-lite fan and thermal clutch. The fan is part #5718 and clutch is #5555. Using this combo and a 180 thermostat with an 1/8" drilled hole, I never, ever have a problem with temperature. I've got a .040 over small block that I can run between 3,400-3,800 rpm on the expressway all day. It also can sit and idle for a parade or a Woodward style traffic jamb. I think I was able to feel the power difference when I changed it. Anyway, it's pretty inexpensive hp.