Fan Drives: Fixed versus Viscous - Free HP

[Ken]

Hot Rod Magazine has a brief article in the April issue where they took a '69 Dodge Dart with a 340 and put it on a chassis dyno to measure the difference in rear-wheel horsepower output when using a fixed fan as opposed to using a viscous drive fan.

How much of a burden on output is a typical flex fan versus a more efficient viscous drive?

In the case of our little Mopar on the Westech chassis dyno, removing the flex fan and installing a clutch fan was worth as much as 5 HP at the rear wheels at points above 5000 engine RPM.

Just thought I'd bring that to our collective attention.

 

[JohnZ]

That's 'cuz almost all thermo-modulated fan clutches essentially disengage over 3500 rpm; been telling people that for years, but most folks don't believe it. I saw the article too - was glad to finally see it in print. Flex-fans just keep sopping up power (and occasionally throw blades...)

 

[72Mako]

I agree guys. In my youth, I ran a flex fan on my vette for awhile. I hated the thing. It sounded like a 747 on take off when the revs came up. A clutch fan corrected that. Charles

 

[78SilvAnniv]

I didn't install a flex fan for horsepower gains. I installed it for cooling issues that I had experienced for years and it has worked great for my application. It solved my run-hot problems instantly.
Heidi