cooling fans robbing power?

I just watched the cooling fan shoot out on MTOD Engine masters show. I had the mindset of Dulcich that fans would not rob any power, though both of us were wrong... granted it was a torque-y SBC chevy that lost power not a low tq 4 pots that I drive. Four types of fans were tested: clutch, plastic flex, aluminium flex, and OEM style. I'll let you watch the show to figure out which was the best/worst.
A comment was made during the show that i found interesting, that the fan would kill the same amount of power on a clapped out motor as it would a 700 HP one. I'm not sure i agree with this, couldn't tell you why either... something about the amount of TQ a motor makes would be a huge factor on how much power it would really rob.
The second is that if his comment is comment is correct that would be HUGE gains on smaller motors for something as simple as removing a fan for an electric one.

If you have MTOD here is a link: https://www.motortrendondemand.com/detail/cooling-fan-shoot-out-/0_olymz420/
kinda a fun epsiode if you ask me

This is what electric fans are for. :)

already looking into it for the opel :)

TurboFocus wrote: A comment was made during the show that i found interesting, that the fan would kill the same amount of power on a clapped out motor as it would a 700 HP one. I'm not sure i agree with this, couldn't tell you why either... something about the amount of TQ a motor makes would be a huge factor on how much power it would really rob.

Makes no difference. A given fan takes a certain amount of power to turn at a certain speed with a certain pressure drop. It doesn't matter what is turning it.

It's why I went electric fan and electric power steering on the racecar.

But an alternator robs power as well. So, electric fan is not a free lunch.

Dusterbd13 wrote: But an alternator robs power as well. So, electric fan is not a free lunch.

And some factory fans will almost make your car stall when they kick on if you dont have some sort of controller that allows it to ramp up.

Depends on the situation, but when I'm dragging my racecar across the vast plains of western Canada in the heat of summer, the sound of that clutch fan spooling up now and then makes me happy. It will draw way, way more air when needed than an electric will, and idles along pretty stress free the rest of the time.

Small car, race car, different attitude.

Dusterbd13 wrote: But an alternator robs power as well. So, electric fan is not a free lunch.

The issue is that most fans are sized so that they flow enough air at low engine speeds. Which ends up being WAY too much at high speeds. Electric fans can deal with this gap a lot better.

Not free, for sure, but certainly better than a mechanical fan.

alfadriver wrote:

Dusterbd13 wrote: But an alternator robs power as well. So, electric fan is not a free lunch.

The issue is that most fans are sized so that they flow enough air at low engine speeds. Which ends up being WAY too much at high speeds. Electric fans can deal with this gap a lot better. Not free, for sure, but certainly better than a mechanical fan.

You can also have a lot more intelligence in the control algorithm. Moving more than 50 mph? Fan is pointless, don't turn it on. With a variable speed fan you can turn it on at a low power level if you only need a little bit of cooling and ramp it up as required. You can also do things like shut down the alternator at WOT and let the battery carry the load for the 10-20 seconds, then charge it back up when the driver isn't demanding full power from the engine (can be hard on the battery as BMW discovered, but...)

Dusterbd13 wrote: But an alternator robs power as well. So, electric fan is not a free lunch.

That's just the thing, though. A belt driven fan will move a lot more air than an electric can. They have to be sized to be able to cool a hot engine down at idle. At higher speeds, it is moving a LOT more air than an electric ever will. It's also sucking a lot more power than an electric ever will.

I'll use my fans as an example because they're the most ridiculously over-motored fans I have seen on anything. They are two-speed, and on high speed the fans pull something like 75 amps. (This is nearly twice as much as the GT500 fan!) Annoyingly barely outside common 30 amp relays and fuse holders There are 746 watts in a horsepower, so this ends up being convenient for head-math since it means all you have to do is divide volts by ten to get horsepower. 1.4 horsepower. if the alternator was even as low as 50% efficient, that's still only 3 horsepower.

I have seen dyno tests where a 16" flex fan drew 44 horsepower. I'm actually somewhat impressed that a V belt could move 44 horsepower, although who's to say that it wasn't slipping?

I can't disagree with any of these statements.

However, with a fan clutch that operates properly, how do the numbers work out?

Asking for homesty here. I run electric fans on everything bu the elky and lawnmower.

I forget those numbers, to be honest. It was a Car Craft article from the 90s or so. (I was gifted a subscription in 1983, when I was five. My family aren't car people but they sure can be enablers. I still kinda miss the collection I used to have)

The numbers still kinda hurt because clutch fans never really fully disengage. There's also the mass that needs to be sped up when accelerating. You can REALLY feel that in a 12A RX-7. Or rather, when you take the clutch fan off and go with an electric, it feels like the engine took off hiking boots and put on some lightweight running shoes. It's more noticable than removing that 23-30lb iron flywheel and replacing it with a 9lb aluminum one.

From a study by GM and I am sure the other Mfg. use the same type of study the engine cooling fan is designed to move the amount of air that is representitive of a car or truck Moving at Thirty MPH, and a clutch fan is represenitive of that. as RPM reach's that point it should disengage, the problem is not engaging below that, and Over heating

Most modern cars use a PWM signal on electric fans to precisely control fan speed. The cars I work on daily have a full 0-99% sweep of fan speed. It's also interesting to watch fan speed and how it correlates to alternator load since the newer alternator are also variable.

I've seen the episode and I'm paraphrasing, but I believe the worst fan was the plastic flex at 24hp draw? Absolute madness.

I'm still a fan (ha ha ha) of electric fans, even though it probably takes horsepower to create the current to turn the fan, for the simple reason that if I'm moving, it is very likely that the fan isn't running at all - I'm driving through air, so I don't need fan.

Also, having the electric fan off helps the engine warm up faster in winter/cold.

How can I watch that episode without a subscription?

As I can't make the link work I am curious about one thing. If the area nehind the radiator is a low pressure area how much air will a fan at 60 mph actually be moving?

I once pulled the little 4 blade nylon fan off the Datsun and the difference wasn't noticeable at all. There may have been a couple of horsepower but the top speed didn't increase at all. Same for lap times.

Tom

there is always the mechanical fan with electric Clutch. I know Fiat toyed with them in the late 60s early 70s, but gave way to fully electric in the middle part of that decade

In reply to mad_machine:

So did Ferrari and Maserati. Cool little electromagnet with a carbon brush. Super simple design, low current draw. I have rebuilt a few and really like them.

I have considered making one out of an ac compressor clutch for the Ford.

Smaller/lower output motors have smaller radiators, smaller fan shrouds, and smaller fans to fit in them. Mechanical fans take power to spin but properly (factory) sized you'll probably find the loss correlates pretty well with the engine's output, a percentage rather than a fixed HP number.

I'm guessing that the clutch fan used the least power.

I also wonder how much you really lose to a directly coupled mechanical fan when actually driving the car, at higher speeds the air getting pushed through the radiator from the motion of the car is going to reduce the amount of work the fan has to do.

In reply to BrokenYugo:

In another episode (possibly an extra) they said they have some pretty serious fans/HVAC in the building. Air flow should be no issue in there

Tom1200 wrote: As I can't make the link work I am curious about one thing. If the area nehind the radiator is a low pressure area how much air will a fan at 60 mph actually be moving?

You may be surprised. Typically the answer is "not much", and even the simplest OEM PCM fan-control strategies have a speed component so the fans wait another 20-30 degrees to kick on at higher speeds.

But I also remember one track day with the RX-7 at Nelson Ledges (there is one point on the whole track where you slow down to about 60, most of the track in that car was a 90mph corner into another 90mph corner, and some 110-115mph straights) and I was running hot. Turning my fan on actually helped cool the engine a bit.

Edit: Unless you meant "how is the fan working in a low pressure area". I have never run a manometer, but I don't think it's a "low pressure" area as much as it is a high pressure in front of the radiator. Again, I've only ever instrumented RX-7s to any meaninfgul degree, but enough air can get pushed through the radiator on a stock ride height, stock airdam '80 model to make the back corners of the hood bow up at higher speeds. Pop the hood latch and the back of the hood would blow up about 3 inches and hover there. I've never witnessed this behavior in the '84-85 style nose cars with their less aggressive airdams. Quantitatively, my air filter is on top of the engine on my '84, and I read a solid 94-95kpa manifold pressure at WOT at all speeds up to about 105-106mph, at which point the quarter mile is over and I stop logging.

Incidentally, thinking about pressure gradients across the radiator a while back made me think of how GM likes to slope radiators top-back on pointy nosed cars like Corvettes and 4th-gen F-bodies. One would think that you'd want the top to be pointed forward, the way post-85 RX-7 and RX-8 do it,, so hot air could naturally rise out of the radiator.

There is probably a bit of a downforce gain by having the high pressure sitting on top of low pressure right out there on the nose, kind of like having a hidden wing in the car.