[MARKDTN]

Car Craft Magazine article, May 2000, page 50 and 51

Dyno test on fans:
alternator, no fan=496 HP
plastic flex fan=460 HP
low profile flex fan=466 HP
High-performance flex fan=476 HP
Rigid steel 6-blade fan=449 HP
Rigid steel 4-blade fan=473 HP
Thermal clutch fan=487 HP
non-Thermal clutch fan=485 HP
HD Thermal clutch fan=476 HP
alternator, electric fan (Black Magic 150)=494 HP

So, stay away from any rigid fans and flex fans. On their engine the clutch fan only used about 10 HP as opposed to 30 for a flex fan. The electric fan only used 2 HP!