Fans - electric vs. mechanical

Opinions?

I'm building a '34 Ford with a 500 bhp 383 Chevy (aluminum heads), TH350 with frame mounted cooler, Griffin aluminum radiator (they say it will cool 600 bhp), Stewart aluminum high flow water pump, NO air conditioning, and a stock hood. I was planning to go mechanical, but now I'm considering electric for the following reasons:

1. Higher fan RPM/airflow at idle where the engine will really need it.
2. Fan only runs when the water temperature requires it, freeing up bhp when the engine is cool.
3. Electrics don't put stress on the water pump bushings.
4. Mechanical fans can reduce airflow at freeway speed. Electrics will freewheel and allow better airflow.

My #1 consideration is keeping my $8,000 motor cool. #2 is getting the motor to cool right the first time so I don't have to fiddle with the car when it's done. #3 is maximizing horsepower output. Fan noise is not a consideration. I can live with the annoying electric fan whine. If necessary, I'll put louvered top panels on the hood, but I'd like to keep it stock. Either way I go, the fan will have a shroud.

Does anybody see holes in my logic? I'd appreciate hearing about your experiences on this subject. Thanks!

Chris

 

elect fans are great,we installed a pair on a friends model a with a blown SBC, tip: wire the fans through a relay with a constant power supply use a 180-190 degree sensor screwed into the water pump to ground the relay, with power all the time the fans will run after shutting down the engine which will help eliminate any boil overs and with the temp sensor mounted up front it is in the airflow of the fans and shuts them off within 5-6 minutes of shutting of the engine

Larry

 

I'm running a thermal clutch fan on the blown big block in my 55, has a good shroud. This eliminates your reasons #2 and 4, and put's a hurtin on #1, since the fan blades on the clutch fans are very aggressive

 

Sounds like you already know the key points:
Saves you up to 17 horsepower.
Cools more efficiently.

No down sides to it except some people think they're ugly.

 

Electrical fans have the other problem of being electric...they need power (lots of it), and when the power goes away they quit working, usually you first notice this when the steam comes out of the radiator

 

Mechanical is more powerful, and if you use a thermostatic clutch there is no downside at all--they freewheel any time they aren't needed. Since you are worried most about idling, get one of the big, agressive 7 blade screws they put on police cars, obviously an older one if you have normal rotation setup.
Think about this: Chevy came up with a mechanical fan arrangement fro the LT-1 powered hot climate police cars of the eighties, an engine that was designed specifically for electric fans and which didn't even have a pump hub to put one on...they came up with a special fan pedestal and drive belt that gave the fan a home.

 

what exactly does a clutch fan do that a regular mechanical fan does not?

 

stolen from wiki:

Fan Clutch refers to an automatic device frequently used in automotive cooling systems. When the engine is cool or even at normal operating temperature, the fan clutch partially disengages the engine's mechanically-driven radiator cooling fan, generally located at the front of the water pump and driven by a belt and pulley connected to the engine's crankshaft. This saves power since the engine does not have to fully drive the fan.

However, if engine temperature climbs beyond the clutch's pre-determined setting, the fan becomes fully engaged, thus maintaining or lowering engine temperature.

Most fan clutches are viscous or "fluid" couplings combined with a bi-metallic sensory system similar to that in a thermostat.

and a picture:

 

I have a 95 LT-1 in my shoebox, I used an electric fan due to the water pump being driven off the cam gear. I was not aware you could put a mechanical fan on it. I will not change from electric to mechanical. I am fond of electric fans. My theory is if a brand new car only has an electric fan, and no mechanical fan, it must be alright. Are you worried about driving a brand new car coast to coast? So don't worry about electric fans, they have been around long enough to be perfected by now. I am all for keeping a car looking old, but if it is not reliable enough to go more than two towns away...

 

I think his point was that Chevy decided that the electric fan could not sufficiently cool the engine under harsh conditions, so they went to a lot of trouble to put a mechanical fan on it. They still put mechanical fans on trucks, too, which need all the cooling they can get.

I agree that electric fans are ok, for many applications. However, with a high hp engine, you need all the cooling you can get, and mechanical fans have an advantage. If the guy were putting a mild 350 in his 34, then I would agree that a good electrical fan would probably be the best choice. He's not, he's putting in a hot rod engine, and needs max cooling.

 

It all depends on how taditional you want your car. If you are loose on that and it's your driver, then an electric fan is pretty handy.

 

If you run a mechanical fan don't run one of those flex fans. I had a 67 Firebird with a 455 10:1 compression ratio and nice bumpy cam. ran about 220 degrees with the Flex fan. its hot here in Cali during the summer.. I put a big stock style clutch fan on it. Made a big difference. I think about 15 degrees or so.....I eventually went to a Rodney Red aluminum radiator with perma cool dual electric fan setup. after that It kept as cool as a stocker..about 180 degrees

 

Some of the flex fans work pretty well, some of them are complete junk.

Look for big, curved blades if you want it to actually cool. The ones with the narrow blades with a sharp bend in them don't work.

 

the largest mechanical fan the will fit in my 31 is 14 inch. it wont keep it cool. i would rather run the mechanical fan but until i can fabricate a decent shroud i am stuck with the electric fan. even then the shroud might not do it for me. it runs about 10 minutes before the temp climbs to 210 after the restart.

 

FWIW--- consider putting a kill switch in your fan circuit if you're only running electric fan(s) with a thermostat switch. I've seen a couple cars where the fans were running while the s____t rods were at freeway speeds, but actually IMPEDING air flow. Cooled the car fine below 45 mph or so... even on hot days. But since the t-stat switch was reading over it's "turn the fan on" setting, it kept the fan on, making the car run hotter when the engine was working harder. We put a master kill switch to turn offf all power to the fan circuit and fixed the problem. If I knew how, it would have been nifty to wire it so that the fan circuit auto-magically got disabled when the car reached a certain speed.

 

"what exactly does a clutch fan do that a regular mechanical fan does not?"
That article explained it pretty well...the reason for the thing is that under most light cruise conditions, the engine is fine without a fan, and the fan becomes just wasted power, wasted noise, and sometimes even significantly obstructs airflow as it reaches speeds beyond its blade design and acts like like a solid disk in the way of the radiator. The clutched fan just freewheels and goes with the flow til its thermostat brings it into action. This also allows use of blade design that is highly effective at idle and in low speed traffic, when you really need a fan.
A book by a mechanical engineer said that engine driven fans were 40% more powerful than a puller electric (not sure exactly how electric fan was specified for the comparison) and perhaps twice that in comparison with a pusher fan!

 

Please tell us about your mechanical fan...size, number of blades, clutch or no, shrouding, location relative to the radiator (usually they sit down too low), etc.

My guess is that you have a marginal mechanical fan setup, and are using the electric fan to make up for it instead of setting up the mechanical fan to do the job all by itself. The mechanical fan was not up to the job, but it was still working....

 

This is a big problem with mechanical fans in early cars with engine swaps, the fan sits too low. In this case a good heavy duty well shrouded electric fan is usually the best choice.

 

This post made me suddenly realize something perhaps of interest here--both Ryan's car ('38 Ford) and the '34 have SLANTED radiators, a problem for proper mechanical fan placement. I would guess a good shroud would be more critical on these vehicles than on cars with vertical radiators.
Note that these radiators also pose a more subtle problem for electric fans!
An electric fan would be parallel to the radiator, but incorrectly angled for the fins and air passages...a mechanical fan would be aligned with the air path, but couldn't be close enough to the radiator unless shrouded...
Aaaagh. Glad I have '32 and '48 Fords and not these strange middle-aged V8's...

 

I would give this serious consideration, but even with a short pump, there isn't enough room. I've used these before on '60s cars with more room and they work just fine even with a pretty well hopped up motor.

Chris

 

You may have to use an electric fan just because of how things fit...not for the reasons you listed in your first post! Just make sure it's a good fan with shrouding and a well designed blade, and be careful with the wiring to make sure it doesn't quit like Ryans did. Probably wouldn't hurt to figure out some way to rig up an idiot light just in case it gets warm.

 

I agree. Things are very tight. And when it comes time to replace the water pump, it will be much easier with an electric. If I go electric, I'll wire in a switch to bypass the t-stat just in case it dies on me. That way I won't be stuck with no fan at all.

Thanks for all the opinions, guys!

Chris

 

I've got an electric pusher in my Hup. My grill shell is only 17 inches wide. The radiator is an old Ford Zodiac unit that is 16" wide and I've got AC to boot. The fan is a 16" unit that covers 90% of the condensor. No mechanical fan at all as the l6 292 was too long. No shroud either. The temp here today is 102 and my engine hit 195 while waiting for 10 minutes in the drive thru at KFC. (Why are they surprised when you order chicken). The highest I've ever seen it so far was just over 200. Of course it was 94 degrees outside and I was traveling 84mph.

 

those 292s sure run cool, don't they?