Typical of articles featured in Car craft.
Fan= electric or clutch?
Melting Slicks
Joined: Aug 2008
Posts: 2,200
Likes: 3
From: Lehigh county Pennsylvania
I've had stock clutch fans. I've had fiberglass fans, and aluminum fans. None has worked as well (or been as quiet) as this Zirgo 16" puller electric fan with 'S' blades. I've got a 180 coolant thermostat and my temp stays there when highway driving without the fan operating. When in stop-n-go traffic, the electric thermostat turns on at 210. Then it only draws 12-15 amps. Who needs a 100 amp alternator for that much draw?
Plenty of cooling for a mild 350 with manual gearbox for southern Indiana area.
Plenty of cooling for a mild 350 with manual gearbox for southern Indiana area.
Le Mans Master
Joined: Nov 1999
Posts: 5,768
Likes: 3
From: San Diego CA
Its interesting that this thread has come up, on Sunday a friend and I went to the Long Beach swap meet, where we met up with another friend. Jeff Smith, Tech Editor from Car Craft magazine.
We were there to look for electric fans, this is why its so coincidental. BTW I managed to pick up the dual SPAL fan/shroud package in excellent shape for $80.
Anyway, while walking around the swap meet Jeff discussed an idea for a fan related article thats been running around in his head, and I mentioned that the ongoing argument we always have here on the forums is which is better (usually for power) electrical or mechanical?
So I sent Jeff a link to this discussion and he responded saying I could post the following if I wanted.
That last sentence pretty much sums it up for me as well, most of us dont drive our cars all that hard and the OP's question dealt primarily with a mild car. So probably in the grand scheme of things it doesnt matter one whit which setup we choose.
They both work, they both have advantages, pick one and enjoy.
We were there to look for electric fans, this is why its so coincidental. BTW I managed to pick up the dual SPAL fan/shroud package in excellent shape for $80.
Anyway, while walking around the swap meet Jeff discussed an idea for a fan related article thats been running around in his head, and I mentioned that the ongoing argument we always have here on the forums is which is better (usually for power) electrical or mechanical?
So I sent Jeff a link to this discussion and he responded saying I could post the following if I wanted.
Eric,
It seems pretty simple - the advantage of the electric fan(s) is that you have airflow on demand when you need it. The rest of the time, the fans are operating at either a reduced rate (with pulse width modulation – PWM – control) or off. I prefer the PWM because you don’t have the cyclical temperatures the engine has to endure. That’s the way the factory does it.
They are also missing the point of electric fans. Yes, the emissions idea is part of it, but it’s actually popular because of mileage. What everyone fails to realize is that the engine has to drive that clutch fan all the time. Even when it is “disengaged” it still requires engine power to drive it. That’s negative work. More importantly for the hot rodder, when the engine is up to temperature (which is ALL THE TIME) the fan is working at a given percentage of draw. So under wide open throttle (WOT) at temperature –the fan is eating HP.
As a test during my rear axle comparison story – I had fitted the Chevelle with a very large 18-inch 7-bladed fan to ensure the engine would stay cool – maximum airflow – with a fan clutch. We had to spray adhesive on the belt before each run to keep the belt from slipping and squealing. After the rear axle tests were over, we pulled the fan off for a quick chassis dyno comparison. Despite the fact that the engine temperature spiked about 20 degrees higher during the test (which costs hp), we GAINED 8 hp at the rear wheels over the test with the fan in place. This is a clutch fan setup. Had I then installed a pair of electric fans to keep the temp down – we probably would have made more yet – even with the fans running with a combined draw of 50 amps. Frankly, 50 amps is nothing in terms of hp draw – perhaps one hp even through the loss of conversion from mechanical to electrical power to driving the fans. Now what I have is a pair of fans that;
A) maintain a constant engine temperature of my choosing
B) I can elect to turn on and off at my choosing not at the whim of the clutch – in other words I now have the control of when and how much the fans run
C) At highway speeds the fans are generally off or one is running at a greatly reduced speed under PWM control
D) I have greatly reduced the noise factor
E) While perhaps the fans weigh the same as a clutch and fan assembly, I don’t have to accelerate that mass when the vehicle is accelerating – hence I have picked up acceleration.
There are probably at least five more reasons why the electric fans are a better idea, most of which deal with control. My buddy in GM tells me that this is where it’s heading with new cars. We have advanced with the basic four-stroke internal combustion engine that future advances will mostly be around controlling what’s happening – i.e. EFI, direct injection, and the like. Clutch fans don’t fit into that scenario very well. Engine-driven fans do have a place where maximum cooling (airflow) is a requirement as with heavy duty trucks.
For those who insist on steadfastly remaining on the mechanical side of things – I say – enjoy.
Jeff
It seems pretty simple - the advantage of the electric fan(s) is that you have airflow on demand when you need it. The rest of the time, the fans are operating at either a reduced rate (with pulse width modulation – PWM – control) or off. I prefer the PWM because you don’t have the cyclical temperatures the engine has to endure. That’s the way the factory does it.
They are also missing the point of electric fans. Yes, the emissions idea is part of it, but it’s actually popular because of mileage. What everyone fails to realize is that the engine has to drive that clutch fan all the time. Even when it is “disengaged” it still requires engine power to drive it. That’s negative work. More importantly for the hot rodder, when the engine is up to temperature (which is ALL THE TIME) the fan is working at a given percentage of draw. So under wide open throttle (WOT) at temperature –the fan is eating HP.
As a test during my rear axle comparison story – I had fitted the Chevelle with a very large 18-inch 7-bladed fan to ensure the engine would stay cool – maximum airflow – with a fan clutch. We had to spray adhesive on the belt before each run to keep the belt from slipping and squealing. After the rear axle tests were over, we pulled the fan off for a quick chassis dyno comparison. Despite the fact that the engine temperature spiked about 20 degrees higher during the test (which costs hp), we GAINED 8 hp at the rear wheels over the test with the fan in place. This is a clutch fan setup. Had I then installed a pair of electric fans to keep the temp down – we probably would have made more yet – even with the fans running with a combined draw of 50 amps. Frankly, 50 amps is nothing in terms of hp draw – perhaps one hp even through the loss of conversion from mechanical to electrical power to driving the fans. Now what I have is a pair of fans that;
A) maintain a constant engine temperature of my choosing
B) I can elect to turn on and off at my choosing not at the whim of the clutch – in other words I now have the control of when and how much the fans run
C) At highway speeds the fans are generally off or one is running at a greatly reduced speed under PWM control
D) I have greatly reduced the noise factor
E) While perhaps the fans weigh the same as a clutch and fan assembly, I don’t have to accelerate that mass when the vehicle is accelerating – hence I have picked up acceleration.
There are probably at least five more reasons why the electric fans are a better idea, most of which deal with control. My buddy in GM tells me that this is where it’s heading with new cars. We have advanced with the basic four-stroke internal combustion engine that future advances will mostly be around controlling what’s happening – i.e. EFI, direct injection, and the like. Clutch fans don’t fit into that scenario very well. Engine-driven fans do have a place where maximum cooling (airflow) is a requirement as with heavy duty trucks.
For those who insist on steadfastly remaining on the mechanical side of things – I say – enjoy.
Jeff
They both work, they both have advantages, pick one and enjoy.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
Your story is one of the examples where 'selected info' is provided to prove a point.
First- 50 amps is not 'nothing' in terms of HP draw:
12V x 50 amp = 600 watts x typical electrical motor efficiency of ~80ish% gives us around 720 watts. 1HP = 750 watts. Alternators are about 50% efficient at best in converting mechanical energy into electrical so that's around 2 HP required to run the fans or recharge the battery if the fans are on during slow speed operation where the alternator is not putting out sufficient current.
Second- it's well known that a clutch fan with the clutch fully engaged will eat up to 10HP at engine red line, no 'news' there. It's also well known that a released clutch allows the fan operate at a mere fraction of it's locked up speed. Consumption figures under those conditions are ~1HP.
Sounds like you friend was operating with a hot engine and locked up clutch, typical of dynpo tests, but sort of an apples and oranges comparison nonetheless. Maybe somebody else should do the electric fan test with a flat battery and fans on full tilt- that would be a more even playing field.
First- 50 amps is not 'nothing' in terms of HP draw:
12V x 50 amp = 600 watts x typical electrical motor efficiency of ~80ish% gives us around 720 watts. 1HP = 750 watts. Alternators are about 50% efficient at best in converting mechanical energy into electrical so that's around 2 HP required to run the fans or recharge the battery if the fans are on during slow speed operation where the alternator is not putting out sufficient current.
Second- it's well known that a clutch fan with the clutch fully engaged will eat up to 10HP at engine red line, no 'news' there. It's also well known that a released clutch allows the fan operate at a mere fraction of it's locked up speed. Consumption figures under those conditions are ~1HP.
Sounds like you friend was operating with a hot engine and locked up clutch, typical of dynpo tests, but sort of an apples and oranges comparison nonetheless. Maybe somebody else should do the electric fan test with a flat battery and fans on full tilt- that would be a more even playing field.
Instructor
Joined: Mar 2009
Posts: 209
Likes: 1
From: Denver CO
My $0.0002,
I have both mechanical and electrical on my setup. Dual electric fans on the radiator, and a 5 blade mechanical reduction fan... not a thermal clutch fan. No overheating ever, and I still have my stock alternator...
It works well.
Danny
I have both mechanical and electrical on my setup. Dual electric fans on the radiator, and a 5 blade mechanical reduction fan... not a thermal clutch fan. No overheating ever, and I still have my stock alternator...
It works well.
Danny
Last edited by Raider74; Oct 12, 2011 at 03:47 PM.
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
Instructor
Joined: Mar 2009
Posts: 209
Likes: 1
From: Denver CO
http://www.summitracing.com/parts/HDA-1705/
Sorry I couldn't remember the term but it is simply a "non thermal" fan clutch. Rather than engaging at a certain temperature as thermal fan clutches do, it simply reduces the fan speed from the speed of the water pump shaft by various percentages for various rpms. As engine speed increases, it disengages more. At idle, its speed is the same as the water pump shaft.
So basically, the higher the rpms go by mechanical means it slows itself down to keep it from flinging the fan apart in your engine bay!
Last edited by Raider74; Oct 12, 2011 at 03:46 PM.
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Burning Brakes
Joined: Mar 2010
Posts: 987
Likes: 7
From: Surrey British Columbia
I made the decision to go dual electrics over a year ago. Proof is in the pudding. Some (not all) guys who kept the old fan/clutch assembly experienced cooling issues. Guys who converted over to electric fans love them and swear by the technology. That's good enough for me.
