Tuner wrote: ↑Thu May 06, 2021 7:44 pm
You really think 30 HP + the water pump through a 3/8" V belt?
Yes. I think so. Sticking your hand out the window at 60mph is quite a force. Now multiply that x 5, 6 or 7 to account for the total area of the fan blades whipping around at 6,000+rpm. It’s dyno proven several times over that mechanical fans can cost that much power. This data isn’t new, this is just the newist test.
The fan clutch is definitely worth the price. 25-30hp is a lot for a street car.
lefty o wrote: ↑Wed May 05, 2021 9:43 pm
dont forget a properly fitting fan shroud.
Fan shroud is a big deal, for sure.
I've noticed many OEM setups have the fan hanging about 1 inch out the back of the shroud. Must be a good reason for it. Only thing I can think of is maybe the air passes though the fan in a somewhat spiral path and when it gets to the edge of the shroud the kinetic energy in the spiral movement would be lost if it went straight out if the fan was entirely inside the shroud. If some of the air is allowed to exit radially from the ends of the fan blades it would act a bit as a centrifugal blower as well as axial.
I have done comparison on a couple of my daily drivers by checking fuel consumption, good working clutch fan to electric on a thermo switch, it was pretty much spot on 1liter/100km over several full tanks on them.
I don't have the exact BSFC for the engines, and you have different rpm (cruising at 2-2500, occasional acceleration up to about 5000 on the one I have now), but it will give an idea on the average difference in power requirement.
looks to me the bottom pulley is about an inch bigger than the pump pulley, I expect an electric fan is going to have a big advantage over any mechanical fan when the engine rpm is 6200 rather than their 5200 test
Tuner wrote: ↑Thu May 06, 2021 7:44 pm
You really think 30 HP + the water pump through a 3/8" V belt?
I definitely believe it. Engine Masters does very repeatable, valid dyno tests. All parameters are kept the same... temps, etc. They can run repeated tests and you can tell they are on point. It's a very interesting series on the motortrendondemand.com site. For $50/yr you can watch anything on the Motortrend channel, as well as all of their other stuff like Engine Masters... all with no commercials. Engine Masters is all Dyno tests, testing all sorts of things. I believe there are 6 seasons of that show so far.
Fuel economy, cooling, and horsepower. All 3 are important to me. Fan design can play a significant role in all 3. The six blade fan was stock in my 71 C20 with a huge radiator. I tried to use it in my Impala with a single row aluminum radiator, and it puller so much air the belts would squeal under acceleration. It does a good job on the test stand when breaking in a cam. The curved blades run quieter, but I don't know if there is an efficiency to the design. I do know that in a stock application the clutch fans keep my cars cool and I don't have to listen to the fan noise. That allows me to worry about all of the other noises. The aluminum radiator in the picture is a Frostbite replacement for the $300 Summit brand radiator that started leaking after 2 years.
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blackford wrote: ↑Thu May 06, 2021 12:49 pm
I'm sorry, but am I the only one who thinks that 30 HP to turn a fan is absurd? So, I would need to take a very powerful 30 HP electric motor that spins the fan up to speed (either directly or by gearing it up) to move the same amount of air as the same fan being spun by an engine? Does that seem reasonable to anyone?
Not reasonable at all, 30 HP is just nuts, yellow journalism. 30 HP = 22371 Watts / 12 V = 1,864.25 Amps. Who wants to try again?
Assuming these tests are accurate, the one thing that might make sense about a fan using up 30 HP is the power required to accelerate the fan up to speed quickly by an engine. I have to believe that steady state power draw for a fan is not that much, especially when you look at very large industrial fans that have 1/2 HP motors that move a lot more air than an automotive mechanical fan, but they do not accelerate the fan up to speed near as fast as a engine driven fan...they take their time spinning up. I know it does not rotate at 6000 rpm or something, but it is much larger than an automotive fan and it is moving a bunch of air. Here is one for example:
Large industrial fans only spin at low rpm... which takes less power. The dyno tests are indeed valid, as they are very particular with what they do. The main thing is to try and discuss 'why'?
Why?
Resistance. Wind resistance which takes power to turn. Not to mention the weight which Im sure has something to do with it, but not enough to worry about as the plastic fan robbed a ton of power and im sure it weighed next to nothing as far as fans go. So we can put weight at the bottom of the equation.
Next I would guess the radiator has a little to do with it. But thats debatable as they ran a test that showed the fan with NO SHROUD and it picked up some but not a lot. That being the case, I would think the resistance to airflow from having to suck through an obstruction. Sort of like sucking through a straw. That might cause the fan to increase resistance but I of course have no data to back that up. It would have been nice to see them do that just to see what the results would be.
So basically we are dealing with one variable, the resistance to the blades of the fan hitting the air its trying to move. Would that mean in motion, the fan is actually taking LESS hp since the headwind from highway speed is making it easier to turn? That would have been another cool test they could have done. Stick a fan in front of the fan to simulate wind and see if that loss goes down.
All I gotta say is it's good I dont have a dyno in my garage... I would be in there night and day asking and answering questions.... Now I really want a dyno room!
The faster you spin the fan above what the oem stock design intended rpm range is, the more and more power the fan will absorb.. @ 7000+ rpm it eats a lot of power. As does the water pump, alternator and power steering pump.
A solid cam racey sbc wants to rev up up... The fan and accessories don't..
F-BIRD'88 wrote: ↑Fri May 07, 2021 5:53 pm
The faster you spin the fan above what the oem stock design intended rpm range is, the more and more power the fan will absorb.. @ 7000+ rpm it eats a lot of power.
As someone already mentioned, fan HP goes up with the cube of the rpm. If a fan takes 10HP at 5000rpm it will take 27HP at 7000rpm. Gets out of hand real fast.
Tuner wrote: ↑Thu May 06, 2021 7:44 pm
You really think 30 HP + the water pump through a 3/8" V belt?
A V belt powers the mowing deck on my 27hp garden tractor, so yeah.
That belt is 1/2 or 5/8 inch wide. How much power goes to propelling the mower vs. turning the blades?
Come on people, look at the 5 HP electric motor on your shop air compressor, do you see two 5/8" belts? A 3/8" V belt is not going to deliver anywhere close to 30 HP and last 50,000 miles.
I am trying to justify this 30 HP usage of a fan. When I look at converting torque to HP, things seem to be a bit more reasonable in my mind. If a fan takes 25 ft-lbs to turn at 6000 rpm then it is taking over 28 HP to run the fan. That seems like a reasonable amount of torque so I can wrap my head around a fan using 30 HP to run...still hard to imagine but OK. I'm getting electric fans ASAP LOL!
65 Mustang FB, 331 custom built with 289 H beam rods and 383W piston, 282S cam, Ported Maxx 180s, T5z, 9" 3.89 gears. ~460HP@6500
