455 with Fixed Fan or Clutch Fan?

[esisson]

I'm in the process of a 455 (Upgrade) from a 350 Rocket. While I know this has been done successfully many times, I have a couple questions for someone who's already been through it. The 455 I bought came with a cooling fan with a clutch configuration. Not sure if it matters but it was an A/C car. I'm in the process of removing my alt. and PS brackets and noticed that the 350 (Non A/C) car has a fixed or (No Fan Clutch) configuration. My questions are these.
1. Which one is better for a daily driver - clutch or no clutch?
2. Will there be clearance issues with my shroud if I use the clutch fan?
3. Will there be much if any power loss if I use the fixed fan?
4. The fixed fan appears to be smaller than the clutch fan - Will this be adequate in keeping the 455 cool?

Thanks ahead for your responses. I greatly appreaciate your help!

[esisson]

Found this on the net this morning. Tells me what I wanted to know.

A fixed fan delays and slows engine warm-up because it's pulling cold air over the engine and radiator as the engine is still not up to temperature and in reality, needs no cooling yet.
A fixed fan also makes lots of noise. Especially when driving on the highway, it tends to beat at the air instead of adjust to any differences.
A fixed fan has no ability to "give" under sudden acceleration or to not "engage" when not needed. Your engine does not always need to have additional cooling - cool nights, cruising down the highway at part throttle and various other situations don't really require the fan to be engaged and spinning 100% of the time. The added drag of having to spin the fan when not needed takes horsepower away that could be used to push the car forward just to thrash at the air.
Converting to a clutch fan addresses each of these points with a very simple and well-proven device - the 100% mechanical thermostatic clutch unit that mounts between the water pump and the fan.

The thermostatic portion allows faster warm-ups and better cold drivability as a result. The clutch allows the fan to "freewheel" (not spin at engine speed) until the engine is up to temperature and the fan is really needed. This means less airflow through the radiator and faster warm-up times. A small bimetallic spring similar to the one in a choke coil is mounted on the front of the clutch where it is exposed to heat from the radiator. When it gets hot enough, it "locks up" the clutch and the fan spins at engine speed to provide full cooling. When it cools off enough, it "unlocks" and allows the fan to "freewheel" once again.
The clutch portion allows the fan to be quieter because it can "freewheel" and adjust it's speed to match that of the incoming airflow through the radiator. It also does this at idle so that the fan, although it is spinning, is spinning at a greatly reduced speed compared to a fixed fan, thus making much less noise.
The clutch portion allow the fan to "give" in cases of sudden acceleration (so it accelerates more slowly) and the thermostatic portion allows the fan to "freewheel" when not needed. This allows a large amount of "freewheeling" at higher engine speeds such as when you are out on the highway and the fan really isn't needed, and the thermostatic portion allows the clutch to freewheel unless the engine is above a certain temperature and the fan is not needed right now because the engine is not warm or is not warm enough to need more airflow through the radiator.
A Word About Electric Fans...

[Oldsguy]

Yes, I agree with all those statements. They were well put. I have heard engines with fixed blade fans and they have sounded like a helicopter approaching.

[71 delta88guy]

Ditch them both and go electric. Nothing like the sound of engine from under the hood and not the fan roar. I've had 2 fans in my 455 delta's for years. No problems,no noise.

[joe_padavano]

I'd use the clutch fan. Electrics for the most part do not move as much air as a mechanical fan. Also, there seems to be a fallacy that electric fans don't put as much of a HP drain on the motor. The reality is that moving the same amount of air requires the same energy, and that energy ultimately comes from the engine. The difference is that a mechanical fan is driven directly and an electric fan suffers the conversion efficiency losses of converting mechanical energy to electric and back to mechanical.

[71 delta88guy]

The amount of time the electric fans are actually running is quite small,the fans driven off the engine are in continual motion so the power loss is continual. The adjustability of the electric fans allows the user to set the maximum temperature the engine will see.I also like the loss of the big ugly fan shroud. Just my opinion.

[Oldsguy]

Actually, clutch operated fans are not in continual motion as mentioned earlier so there is not a continual loss. The alternator is always being driven by the engine whether there is a demand for energy upon it or not so the argument about continual power loss could be made against the electrically driven fans as well. I am not making that statement just suggesting there is a possibility. I read a thread at ROP about this subject and someone claimed that when his electric fans kicked in during night when the headlights were on that it put such a load on the alternator it dimmed the headlights. Truthfully, I doubted it but can't dispute it, he was there. I think the amount of parasitic power loss from either source (mechanical or electric) is negligable (and un-avoidable) unless we are talking about a vehicle where you are trying to preserve every ounce of energy to make the vehicle go as the case would be in a drag car or in a high mileage competition at MIT.

[joe_padavano]

Originally Posted by Oldsguy

I think the amount of parasitic power loss from either source (mechanical or electric) is negligable (and un-avoidable) unless we are talking about a vehicle where you are trying to preserve every ounce of energy to make the vehicle go as the case would be in a drag car or in a high mileage competition at MIT.

That's correct. An old drag racing trick is to run a switch in the alternator circuit to turn it off during a run. The HP savings is tiny, but every little bit helps. Same for an electric fan - for 12-13 sec you can do without. This is just like the A/C clutch cutout at W.O.T. on virtually every car on the road.

[71 delta88guy]

Yes clutch fans are not constantly engaged, thus the power loss from them is small as long as they are not engaged when power is needed the most. Again, we are not talking about a drag car. However, isn't it nice to be able to know for certain at what temp the fans come on? Also being able to shut them off depending on how it's wired and what situation you're in. Clutch fans offer no such choice and fixed fans just plain suck-power and noise wise. Auto manufacturers have not switched to electric fans for the fun of it. They want to squeez every tenth of a mpg they can from their cars. After you get up to 15 miles per hour a fan is not needed-as long as the cooling system is working properly.I really can't understand the posts in favor of a engine driven fan.My 79 f100 with a 5.0 from a 90 gt mustang had a electric fan. It was on about 9 times in 2 1/2 years. All were in traffic for extended periods of time.

[#1CutlassSupreme]

Originally Posted by 71 delta88guy

...Auto manufacturers have not switched to electric fans for the fun of it. They want to squeez every tenth of a mpg they can from their cars. After you get up to 15 miles per hour a fan is not needed-as long as the cooling system is working properly.I really can't understand the posts in favor of a engine driven fan.My 79 f100 with a 5.0 from a 90 gt mustang had a electric fan. It was on about 9 times in 2 1/2 years. All were in traffic for extended periods of time.

I would agree that power loss results from both kind of fans, but to assert that car manufacturers switched away from metal engine driven fans purely for efficiency is a bit of a stretch. Most asian vehicles engines are set in the compartment sideways which would make a mechanical fan nearly impossible or cost prohibitive to install. You also have to consider the cost of raw materials such as manufacturing metal fans, clutches, and brackets compared to the cost of lighter polymers and plastics.

I'm sure HP and MPG efficiency were considerations, but I'd bet a lugnut that cost was the main driver for change.

[Oldsguy]

Originally Posted by 71 delta88guy

...I really can't understand the posts in favor of a engine driven fan.

Old guys like me change our habits slowly I guess
Actually I have a good reason. In my '46 I don't want the electric fans to detract from the old car, old engine appearance. Even with a modern (well comparitively speaking) engine like a 455. I have tried to keep the modern stuff out of site or not use it at all. By the way, this subject is discussed daily ad-infinitum over at the HAMB where "Old Skool" is supposed to rule supreme yet people have streed rods with moder A/C, or radial tires, or door poppers, or hidden MP3 players, or dual master cylinder brakes systems, or bags, or disc brakes, on and on and on.

[joe_padavano]

Originally Posted by 71 delta88guy

Auto manufacturers have not switched to electric fans for the fun of it. They want to squeez every tenth of a mpg they can from their cars. After you get up to 15 miles per hour a fan is not needed-as long as the cooling system is working properly.I really can't understand the posts in favor of a engine driven fan.My 79 f100 with a 5.0 from a 90 gt mustang had a electric fan. It was on about 9 times in 2 1/2 years. All were in traffic for extended periods of time.

As noted above, it's hard to run an engine driven fan on a transversely mounted engine. Even on north-south engines, there are other considerations. My late model truck still has an engine-driven fan with a monster clutch. The clutch allows the fan to freewheel when not needed, same as an electric. Other RWD cars may have engine compartment length constraints, which mandate the use of an electric fan in front of the radiator. The design of a car is a compromise.

Again, I'm not saying the there's anything wrong with an electric. I'll just stick with a 7 blade mechanical and a clutch on my big block, thanks all the same.