Flex fan or clutch fan

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moparker

moparker

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Sorry if this is a silly question. Which cools better? Flex or clutch. I have a 71 Duster 340. It is modified. Not stock. Thanks for your input.
 
Depends on the pitch of the blades, temperature range of the clutch thermostat, diameter, blade count, all sorts of factors. Usually the flex fans have a more aggressive pitch, meaning they move more air at low engine speeds, then they flatten out at high engine speeds. Note that engine speed does not directly correlate to the need for cooling, although typically, the most critical situation is with the englne idling and the vehicle at a standstill. The clutch fan blades typically are similar to a fixed fan's blades — the difference is that the clutch slows the rotation at high engine speeds as a way to conserve horsepower. The clutch fan does not improve cooling vs. a fixed fan with the same blade count and pitch — what it does is enable using a more aggressive fan profile without costing as much HP to drive it at high speeds. So your typical clutch fan has more or bigger blades, possibly with a more aggressive pitch, than a fixed fan. I realize this does not answer your question, but that is because the question is a little too simple.

That said, I recently installed a clutch fan on my 273 Commando. It had been equipped with a large 7-blade fan from a 383 — it never overheated, but it moved so much air even at idle that I felt it was costing me HP. The clutch fan has similar blades, though only 6 of them. So far the clutch fan seems to perform adequately, but it hasn't faced a hot weather test yet. I also installed a Texas Tornado flex fan on my slant six. I wasn't convinced that the 4-blade fan was adequate for CA summer weather — it sat well away from the radiator and there was no shroud, and the temp used to climb on 90º days. The power steering pulley prevents using a larger diameter fan of any configuration. In use, the flex fan seems to work very well, keeping the gauge dead steady. So there is some real world experience.
 
mvh said:
Depends on the pitch of the blades, temperature range of the clutch thermostat, diameter, blade count, all sorts of factors. Usually the flex fans have a more aggressive pitch, meaning they move more air at low engine speeds, then they flatten out at high engine speeds. Note that engine speed does not directly correlate to the need for cooling, although typically, the most critical situation is with the englne idling and the vehicle at a standstill. The clutch fan blades typically are similar to a fixed fan's blades — the difference is that the clutch slows the rotation at high engine speeds as a way to conserve horsepower. The clutch fan does not improve cooling vs. a fixed fan with the same blade count and pitch — what it does is enable using a more aggressive fan profile without costing as much HP to drive it at high speeds. So your typical clutch fan has more or bigger blades, possibly with a more aggressive pitch, than a fixed fan. I realize this does not answer your question, but that is because the question is a little too simple.

That said, I recently installed a clutch fan on my 273 Commando. It had been equipped with a large 7-blade fan from a 383 — it never overheated, but it moved so much air even at idle that I felt it was costing me HP. The clutch fan has similar blades, though only 6 of them. So far the clutch fan seems to perform adequately, but it hasn't faced a hot weather test yet. I also installed a Texas Tornado flex fan on my slant six. I wasn't convinced that the 4-blade fan was adequate for CA summer weather — it sat well away from the radiator and there was no shroud, and the temp used to climb on 90º days. The power steering pulley prevents using a larger diameter fan of any configuration. In use, the flex fan seems to work very well, keeping the gauge dead steady. So there is some real world experience.
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Thanks for your input. Really appreciate it.
 
Guy's, MotorTrend has a video of dyno tests on most fans. Must watch video. it's very good info. I think there is like 53 sessions now. Good luck.
 
Go with the clutch fan...

I've heard horror stories of flex fans grenading...
 
It depends on the type of solid fan. The factory solid fans were REALLY good. How much HP does a solid fan really take? 5-7 ? MAYBE? I agree the clutch fan is really good. Great compromise between max cooling and mileage and power saving. But if you HAVE a good factory solid fan don't be afraid to use it. Especially if you don't have room for a clutch fan.
 
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