Has anyone ever measured how much parasitic horsepower is being consumed by the belt-driven fan?

I'm curious to know how much of an improvement in fuel economy could be found by removing the fan.

Read this series of dyno runs, where Chris pulled the fan off.....
http://slantsix.org/forum/viewtopic.php ... highlight=

In terms of mileage, it is worth 2 mpg on my Dart.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

This will depend a lot on what MPG you are starting at. I saw very little if any difference when I went from solid fan to electric when I was getting 18-20 MPG w/64 and 68 Darts, but I have not tried to go back to solid now that I am in the 23-26 MPG range. Would be an interesting experiment. Needs to be back-to-back or I won't believe it.

Lou

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Home of Slant6-powered fun machines since 1988

Good point, did just that last summer on a couple of trips, lost 2 mpg from 25 mpg to 23 by going back to a solid fan.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

I saw Chris' dyno results but I must have missed the fan tests. It looks like tests 4A, 4B, 4D and 5A, 5B, 5D would be most applicable.

Comparing Maximum Hp results, we have:

5A-4A = 2.669 hp
5B-4B = 1.553 hp
5D-4D = 1.561 hp

Using Ted's fuel economy results and assuming he gets these fuel economies at 65 mph, his fan consumes about 10 hp (25,684 BTU/hr) in fuel. If his engine's thermal efficiency at the rear wheels is 25%, his fan is absorbing about 2.5 hp while if it's 20% at the rear wheels, his fan is absorbing about 2 hp. Presumably, Ted used the factory 4-blade fan rather than the Summit 5-blade clutch fan as his solid fan.

If gas is $4/gallon and Ted drives 10,000 miles/year, that 2 mpg difference in fuel economy means that the electric fan saves Ted $139/year.

Frank,

Yes, on the stock 4 blade. It was quicker to install than the 5 blade clutch fan for the test. Yes, on the speed when I can. Back roads along the foot hills are at 50 to 60 mph, freeway 65 and 70 when legal.

Fuel savings is actually higher, since I keep the fans armed after shut off. They run a few more minutes until the top tank cools and to keep the carb cool during heat soak and there is no lost fuel through gas percolation or vaporization.

This also eliminates the need to put your foot to the floor on restarts. I just turn the key and the engine lights off. Much more efficient restarts!

I know that was an example estimate but, I drive more than 10,000 miles a year here in the Puget Sound. That is about 1/2 of the years traveling minus trips over the mountains. I usually hit 22 to 26,000 miles a year.

Bottom line, it more than paid for the cost of the fans, thermostatic switch and relay wiring in the first year. I have been running electric fans on the SL6 for over 6 years now. This year I had to replace the first relay.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Hi Frank, another very good reason for using an electric fan, no matter how much power gain you have; leaning over the stock unshrouded propeller on a running engine can scare the pants off anyone!
Take a look at this also:
Check that fan!!!

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Aspenized

I've been corresponding with SSDan about my electrical upgrades and he commented to about this topic. He feels that a 2 mpg gain in fuel economy by switching to an electric fan is a bit optimistic and I would have to agree with him.

SSDan feels that the airflow from the forward motion of the car across the fan at highway speeds would significantly reduce (possibly eliminate) any parasitic load from a mechanical fan.

If we look at Dyno Tests 4A & 5A, there is 2.669 hp difference in power between the 2 fans and 1.553 hp comparing test 4B & 5B. It is not clear to me if the electric fans were running during this time, which would have made the difference between mechanical and electric fans slightly greater.

Assuming that the electric fan was off, my guess is that that the maximum hp occurred at around 5000 RPM. My car with P195/75R14 tires and 2.76:1 axle runs around 2500 RPM at 60 mph, which is half the max hp speed. Since fan power varies with the cube of speed, that 2.669 hp consumption at 5000 RPM would translate to 0.33 hp at 2500 RPM. In gasoline consumption, that would be closer 1.65 hp (20% thermal efficiency). Using 1.553 hp of fan power, this works out to 0.97 hp. If I'm starting off with 23 US mpg, the improvement works out to 1.7 or 0.97 mpg. If I'm starting off with 21 mpg, the improvement works out to 1.4 or 0.8 mpg.

The only other similar discussion I came across about fan hp was this one:
Ecomodder - Electric vs Belt-Driven Cooling Fan

In this Sonoma's case, the clutch fan was calculated to consume about 1 hp at 2500 RPM.

It would be difficult to see any improvement in fuel economy from an electric fan with just a few fill-ups as the improvement can be within the normal variance.

Over 5,000 miles it does make that much difference. I don't think your factoring in how much fuel is lost in heat soak over the many heat cycles with the stock factory fan.

With the electric fan there is no fuel smells when returning to your car from heat soak during each stop. The electric fan will cool the carb and intake during heat soak and eliminate the fuel loss by stopping percolation and vaporization loses plus holding your foot to the floor during hot restarts. So it is more than just parasitic drag that you need to factor for mileage.

It is nice to restart the engine by barely touching the key and not pushing on the gas pedal and have it instantly be idling a 600 rpm.

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Aggressive Ted

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74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

I know your speaking of fuel "economy" ( and a 1mpg increase on a typical slant six would be roughly a 5 percent improvement!) , but how's about economy from increased engine life due better cooling? I would imagine as Ted mentioned,less heat soak,easier starts,less fuel washing oil from bores and causing wear,not to mention running the engine at ideal operating temps must all be reasons to go electric. Lets face it,the factories went from fixed fans to large clutch fans ,then of course electric,I'm sure they did it for very valid reasons. I would have thought the fixed fan is a similar to an aircraft prop,as rpm increases beyond its design range efficiencies can drop off ( the design range is very very narrow,2000 to 2500 rpm typical),yes sure the angle of attack hence drag will change as airflow is increased (at highway speeds its hardly a game changer ),and yes the diameter,hence tip speed of the fan is much smaller compared to a prop,but without the ability to vary the blade angle of the fan it's a really basic bit of gear,im sure Mopar or any other manufacturer never spent much time on blade designs! Electric fans running at their ideal rpm must make them a more efficient means of moving air.

Plus electric fans can be quieter if the proper blade design is used or when the electric fan is off. This may not matter to some people, but I like a quiet running vehicle.

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Casually looking for a Clifford hyperpak intake for cheap.

I have been following this post with interest. My factory four blade fan beats the air between 2500 and 3100 rpm when out on the open highway. It has to be sapping horse power right off the top before any mechanical energy gets transmitted to the rear wheels. I have no idea where the design speed of said fan is, but where all modern automobiles are assembled with electric fans their ubiquitous use has to be for fuel economy reasons, even though most modern drive trains only turn at around 2000 rpm at highway speeds.

I’m about to try Ted’s duel 10 inch fan recipe now that I discovered he is using the stock 18 inch radiator.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

SlantSteve touched on another thought about economy. Not only for cooling but also on warm ups! The electric fan allows the engine to come up to temp much quicker and run more efficiently. Since SL6's have a very efficient cooling system, not having a fan blowing cold air over the engine first thing in the morning, the engine block and intake manifold can warm up much faster. This helps the intake manifold to atomize the fuel better which helps on cold throttle response and over all power from a cold start. Since there isn't a constant blast of cold air blowing over the engine the stock choke disengages much sooner which helps on fuel economy. I know in winter the engine heater puts out heat much quicker with out the fan. In fact some winter days the fans never ever turn on and that includes hard freeway driving and lots of stop and go. I find that I can run a couple of jets sizes smaller and still have excellent power and spunk off the line.

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Aggressive Ted

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74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Very good point Ted, living in a warmer climate I didn't consider the warm up cycle as well.... Poor atomization is very detrimental to engine wear and mileage.... It's a big ask for that fixed fan to cope with all the variances the average car sees in climate, driving style,vehicles use etc etc. A minimum of 5 percent increase in mileage is a good deal in my book,especially for a relatively easy,low buck modification!

That would only be true in an instance where the angle of attack (propeller blade angle vs. wind speed) matched the windspeed exactly.

The turbulent conditions behind the radiator will put a strain on the fan blades at any vehicle speed. Easy to find out: Run the car with and against the wind at several speeds, is there a 'soft spot' in any speed against the wind, where the fuel consumption actually drop because of less resistance from the fan?

Edited: It may depend to a certain degree on the presence of a tight-fitting fan shroud at the ideal engine speed/wind speed, but would at the other hand probably increase drag at low speed because more area of a fan blade is used to move air, due to the confined space around the fan.

A comparison of drag with a shrouded vs. unshrouded fan would be very interesting to see.
A very good point for us 'northerners'.

Olaf

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Aspenized