LilYellowZQ8
12-07-04, 08:12 PM
Written by Jedi Master.
Free horsepower. That's what removing the cooling fan from your engine has often been called. Running without the fan is fine for drag racing, but what about your everyday commute? We wanted to find out just how much power it really takes to spin that mechanical fan, so we tested seven different fans on the dyno. We first baselined the engine without a fan, then tried a stock non-flex O.E.-type fan, three different flex fans, and two clutch-controlled fans.
Looking at the power figures, you'll note that the engine made almost equal peak power when equipped with a thermostatically controlled clutch fan as it did using no fan at all. That's because the air temperature in the dyno cell never got hot enough to engage the clutch as it would have mounted behind the radiator in a car. So, the power numbers we saw may be a bit high for the thermo-controlled clutch fan.
The seven-blade non-flex O.E. fan we tested was representative of fans installed on early low-performance passenger cars. It allowed decent low-end power up to 3,000 rpm. Above that, power began to drop off as the non-flex fan put increased loads on the engine. We also tested an inexpensive plastic flex fan, an aluminum blade flex fan, a heavy-duty stainless steel flex fan, and an OEM clutch fan designed to uncouple above a certain rpm. The rpm-activated clutch fan outperformed all the flex fans tested but was inferior to the fixed-blade O.E. fan below 3,500 rpm. In conclusion, the best power can still be made with no fan at all. Short of this, a thermo-controlled clutch fan is the best choice for optimum power and cooling capacity. CHP
Electric fans are an often discussed modification on the various forums. Unfortunately, it seems that there is also a lot of inaccurate information surrounding the "e-fan" and how it should be installed. This document will hopefully answer some of the most common questions with regards to e-fans, and debunk some of the myths.
Before we begin, let's just take a general overview of the cooling system. Forget for a moment that there is also an oil cooler. We will just concentrate on the water cooling system.
The cooling system consists of 5 basic parts: the engine, the water pump, the radiator, fan and the thermostat. Water passages inside the engine are filled with a coolant/water mixture (commonly just called "coolant"). These passages allow the heat that is generated within the engine to transfer into the coolant. Coolant is circulated through the engine via a water pump, which is driven from a belt off of the main eccentric shaft pulley. The stock fan and fan clutch assembly also mounts of the shaft of the water pump, and is therefore driven by the engine as well. The pump's job is to circulate water though the engine and the radiator. Air flowing over the radiator cools the coolant, and thus the engine. A thermostat is used to open or close flow of coolant through the rad to maintain the engine temperature at a constant (195 F).
Now that we know how the cooling system works, let's be clear about the function of the fan, and how the clutch assembly works. As mentioned, the stock clutch fan is attached to the water pump shaft. This shaft receives it's rotation from the engine itself. The fan is not directly attached to the shaft, it is actually bolted to a viscous clutch. The clutch then sits between the fan and the shaft. The purpose of the clutch is to keep the fan at a (fairly) constant speed, and to only engage the fan when it is needed. Think of the clutch as a very simple mini torque converter. Inside is a fluid. When this fluid is cool, the clutch is freewheeling, and thus the fan turns relatively slowly as the clutch slips. As the engine heats up, so does the clutch as hot air from the rad flows over it. The fluid thickens up, engaging the clutch and turning the fan at engine speed up to about 2000 RPM. At this point, it begins to slip again to keep the fan at the most efficient speed. Thus, more air flows through the rad, cooling the engine. The clutch cools down as the engine does, and then disengages. Thus, the cycle repeats.
What's "important to note" is that the fan is only used when the engine is idling, or the car is creeping along at low speed (less then 20 MPH). If the car is stationary or creeping, there is not enough natural airflow through the rad to provide adequate cooling. Thus, the necessity of a fan. Against popular myth a thermal clutch fan, it does not turn on when it gets hotter. Once the underhood temps have risen to over 120, the unit is activated. Simlilar RPM clutch fans run all the time and are RPM freewheeled, the difference between the 2 is a thermal unit will not run until temps are over this temp threshold, which allows a no fan faster warmup.
By far, the most common misconception is that the electric fan cools better then the stock. People see the high CFM numbers in the catalogues (for example, the Black Magic is advertised as pulling 2,800 CFM, and the Perma Cool "finger chopper" is advertised at 2,950 CFM) and are impressed. The truth is that no one actually knows the CFM rating of the stock fan. It has simply never been measured by anyone in the aftermarket and listed. All we do know is that it is rated at "a lot", more times than not it will exceed 4000 CFM. And to be honest, who cares how much air the stock fan moves? It is more then adaquate as long as it's clutch and the rest of the cooling system is in good shape. The steeply raked blades of the stock fan move quite a lot of air, even if it turns slower then an aftermarket electric unit. Experience has shown that when in good shape, the stock fan is even easily capable of handling a 400HP engine. How much power do you make?
Many people also seem to believe that an electric fan will cure their "at speed" overheating problems. Recall that the fan is not even used when at speed, as the natural flow of the of air through the radiator is more then enough (much more then a fan, in fact) to keep the car cool.
Of course, you're not necessarily after better cooling. You've seen those TV commercials or catalogue ads that promise "Up to 17 free HP!" by converting to an electric fan. Well, that's simply not true. There will be a horsepower gain for sure, on the order of 0.5 - 5HP, with 17 H.P. reserved for big V-8s using 40 lb fans at 6000 rpms. But remember that the electric power to run the fan must come from somewhere, and that somewhere is the alternator. Electric fans draw quite a lot of current. Most pull surges of 35A or more to start up, then run at 8A-10A. This puts extra load on the alternator. Ever pedaled a bicycle with a generator powered light? If so, then you will know that as the electrical load on a generator/alternator increases, the generator/alternator becomes harder to turn. Suddenly, all that "free" HP you just freed up is once again being used. This time, though, it is being used to turn the alternator. There is also an inefficiency in the whole system. We are converting mechanical energy, to electrical energy, to mechanical again to run the fan. This very inefficient, much less then just driving the fan directly via the mechanical energy of the rotating shaft.
We can see that the electric fan is a large current draw. The normal S alternator is rated at 80A, non A/C ed, others up to 120A . Real world tests have shown that actual output is somewhat less then the specifications would indicate. Add the load of the electric fan, and you are that much closer to overloading an already factory-stressed electrical system.
While on the subject of the electrical system, let's look at how the fan is actually connected. The proper way to control an electric fan is via a thermostat and relay combination (fused, of course). Unfortunately, very few people actually do this. Many installations simply connect the fan to run all the time, or to a switch inside the car. In the latter case, your brain actually becomes the thermostat. Needless to say, this is a very poor arrangement as it is easy forget to switch on the fan as the temperature climbs. Worse still, the S temperature gauge is horribly inaccurate. By the time you see it move, the car is already too hot. Leaving the fan on all the time presents a different set of problems. It becomes an unnecessary drain on the system, and may actually over cool the car. This is not necessarily a flaw of the fan itself, but of the installer.
Lastly, there is the question of reliability. The stock clutch fan can have two failure modes: the clutch will fail, or the fan will physically break. The electric fan introduces many more failure points: fuse, all wiring connections, physical failure of the fan, failure of the motor, failure of the thermostat.
By now, you're probably wondering "Gee, why is this guy so against electric fans?". Well, I'm not really. But I recognize their disadvantages. There are also some useful advantages to the electric fan.
Since you are no longer tied to the shaft of the water pump, the electric fan can be oriented in any way, and moved around to make space. Without the stock fan shroud in the way, there is much more room in the engine bay, as well as room to route things like intercooler piping, cold air intakes, etc. An electric fan may also be required when going to certain aftermarket radiators that do not have provision for mounting the stock fan shroud.
Free horsepower. That's what removing the cooling fan from your engine has often been called. Running without the fan is fine for drag racing, but what about your everyday commute? We wanted to find out just how much power it really takes to spin that mechanical fan, so we tested seven different fans on the dyno. We first baselined the engine without a fan, then tried a stock non-flex O.E.-type fan, three different flex fans, and two clutch-controlled fans.
Looking at the power figures, you'll note that the engine made almost equal peak power when equipped with a thermostatically controlled clutch fan as it did using no fan at all. That's because the air temperature in the dyno cell never got hot enough to engage the clutch as it would have mounted behind the radiator in a car. So, the power numbers we saw may be a bit high for the thermo-controlled clutch fan.
The seven-blade non-flex O.E. fan we tested was representative of fans installed on early low-performance passenger cars. It allowed decent low-end power up to 3,000 rpm. Above that, power began to drop off as the non-flex fan put increased loads on the engine. We also tested an inexpensive plastic flex fan, an aluminum blade flex fan, a heavy-duty stainless steel flex fan, and an OEM clutch fan designed to uncouple above a certain rpm. The rpm-activated clutch fan outperformed all the flex fans tested but was inferior to the fixed-blade O.E. fan below 3,500 rpm. In conclusion, the best power can still be made with no fan at all. Short of this, a thermo-controlled clutch fan is the best choice for optimum power and cooling capacity. CHP
Electric fans are an often discussed modification on the various forums. Unfortunately, it seems that there is also a lot of inaccurate information surrounding the "e-fan" and how it should be installed. This document will hopefully answer some of the most common questions with regards to e-fans, and debunk some of the myths.
Before we begin, let's just take a general overview of the cooling system. Forget for a moment that there is also an oil cooler. We will just concentrate on the water cooling system.
The cooling system consists of 5 basic parts: the engine, the water pump, the radiator, fan and the thermostat. Water passages inside the engine are filled with a coolant/water mixture (commonly just called "coolant"). These passages allow the heat that is generated within the engine to transfer into the coolant. Coolant is circulated through the engine via a water pump, which is driven from a belt off of the main eccentric shaft pulley. The stock fan and fan clutch assembly also mounts of the shaft of the water pump, and is therefore driven by the engine as well. The pump's job is to circulate water though the engine and the radiator. Air flowing over the radiator cools the coolant, and thus the engine. A thermostat is used to open or close flow of coolant through the rad to maintain the engine temperature at a constant (195 F).
Now that we know how the cooling system works, let's be clear about the function of the fan, and how the clutch assembly works. As mentioned, the stock clutch fan is attached to the water pump shaft. This shaft receives it's rotation from the engine itself. The fan is not directly attached to the shaft, it is actually bolted to a viscous clutch. The clutch then sits between the fan and the shaft. The purpose of the clutch is to keep the fan at a (fairly) constant speed, and to only engage the fan when it is needed. Think of the clutch as a very simple mini torque converter. Inside is a fluid. When this fluid is cool, the clutch is freewheeling, and thus the fan turns relatively slowly as the clutch slips. As the engine heats up, so does the clutch as hot air from the rad flows over it. The fluid thickens up, engaging the clutch and turning the fan at engine speed up to about 2000 RPM. At this point, it begins to slip again to keep the fan at the most efficient speed. Thus, more air flows through the rad, cooling the engine. The clutch cools down as the engine does, and then disengages. Thus, the cycle repeats.
What's "important to note" is that the fan is only used when the engine is idling, or the car is creeping along at low speed (less then 20 MPH). If the car is stationary or creeping, there is not enough natural airflow through the rad to provide adequate cooling. Thus, the necessity of a fan. Against popular myth a thermal clutch fan, it does not turn on when it gets hotter. Once the underhood temps have risen to over 120, the unit is activated. Simlilar RPM clutch fans run all the time and are RPM freewheeled, the difference between the 2 is a thermal unit will not run until temps are over this temp threshold, which allows a no fan faster warmup.
By far, the most common misconception is that the electric fan cools better then the stock. People see the high CFM numbers in the catalogues (for example, the Black Magic is advertised as pulling 2,800 CFM, and the Perma Cool "finger chopper" is advertised at 2,950 CFM) and are impressed. The truth is that no one actually knows the CFM rating of the stock fan. It has simply never been measured by anyone in the aftermarket and listed. All we do know is that it is rated at "a lot", more times than not it will exceed 4000 CFM. And to be honest, who cares how much air the stock fan moves? It is more then adaquate as long as it's clutch and the rest of the cooling system is in good shape. The steeply raked blades of the stock fan move quite a lot of air, even if it turns slower then an aftermarket electric unit. Experience has shown that when in good shape, the stock fan is even easily capable of handling a 400HP engine. How much power do you make?
Many people also seem to believe that an electric fan will cure their "at speed" overheating problems. Recall that the fan is not even used when at speed, as the natural flow of the of air through the radiator is more then enough (much more then a fan, in fact) to keep the car cool.
Of course, you're not necessarily after better cooling. You've seen those TV commercials or catalogue ads that promise "Up to 17 free HP!" by converting to an electric fan. Well, that's simply not true. There will be a horsepower gain for sure, on the order of 0.5 - 5HP, with 17 H.P. reserved for big V-8s using 40 lb fans at 6000 rpms. But remember that the electric power to run the fan must come from somewhere, and that somewhere is the alternator. Electric fans draw quite a lot of current. Most pull surges of 35A or more to start up, then run at 8A-10A. This puts extra load on the alternator. Ever pedaled a bicycle with a generator powered light? If so, then you will know that as the electrical load on a generator/alternator increases, the generator/alternator becomes harder to turn. Suddenly, all that "free" HP you just freed up is once again being used. This time, though, it is being used to turn the alternator. There is also an inefficiency in the whole system. We are converting mechanical energy, to electrical energy, to mechanical again to run the fan. This very inefficient, much less then just driving the fan directly via the mechanical energy of the rotating shaft.
We can see that the electric fan is a large current draw. The normal S alternator is rated at 80A, non A/C ed, others up to 120A . Real world tests have shown that actual output is somewhat less then the specifications would indicate. Add the load of the electric fan, and you are that much closer to overloading an already factory-stressed electrical system.
While on the subject of the electrical system, let's look at how the fan is actually connected. The proper way to control an electric fan is via a thermostat and relay combination (fused, of course). Unfortunately, very few people actually do this. Many installations simply connect the fan to run all the time, or to a switch inside the car. In the latter case, your brain actually becomes the thermostat. Needless to say, this is a very poor arrangement as it is easy forget to switch on the fan as the temperature climbs. Worse still, the S temperature gauge is horribly inaccurate. By the time you see it move, the car is already too hot. Leaving the fan on all the time presents a different set of problems. It becomes an unnecessary drain on the system, and may actually over cool the car. This is not necessarily a flaw of the fan itself, but of the installer.
Lastly, there is the question of reliability. The stock clutch fan can have two failure modes: the clutch will fail, or the fan will physically break. The electric fan introduces many more failure points: fuse, all wiring connections, physical failure of the fan, failure of the motor, failure of the thermostat.
By now, you're probably wondering "Gee, why is this guy so against electric fans?". Well, I'm not really. But I recognize their disadvantages. There are also some useful advantages to the electric fan.
Since you are no longer tied to the shaft of the water pump, the electric fan can be oriented in any way, and moved around to make space. Without the stock fan shroud in the way, there is much more room in the engine bay, as well as room to route things like intercooler piping, cold air intakes, etc. An electric fan may also be required when going to certain aftermarket radiators that do not have provision for mounting the stock fan shroud.