Corvette Engine Fan - Tech
Defining Which Fan You Should Use In Your Corvette
June 16, 2010
By Wayne Scraba
Photography by Wayne Scraba
In contrast to the '66 L72,...
In contrast to the '66 L72, check out this '67 L88. It's common knowledge that these cars came without fan shrouds. The idea here was to discourage use on the street (as if a lumpy cam, 12:1+ compression ratio and a decided lack of creature comforts wasn't enough). Yes, it's neat to look at, but in practice, operating a Corvette on the street without a tight fitting shroud is just asking for heating trouble.
In the hypothetical world, a fan wouldn't be required if a Corvette was constantly driven at high speeds (definitely an enticing concept, but not too practical). Airflow from the vehicle's velocity would be sufficient to allow for adequate airflow over the radiator surface, with the result being proper cooling. After all, that's pretty much how World War II aircraft with liquid cooled engines worked (good examples being the P-51 Mustang, Spitfire, Warhawk, and so on). While this would be an ideal situation, it's seldom possible-or realistic. Because of this, a fan of some sort becomes a necessary evil.
Given the fact that a fan is pretty much an essential commodity, it's probably a good idea to install one that actually works. There are a number of good quality fans on the market, and they range from OEM, factory produced models to stainless steel flex versions, and of course, electric jobs that are so common on late-model Corvettes and used with regularity on many Vette Rods. The typical "standard" fan assembly is fixed. It rotates constantly with the water pump shaft. A thermostatic fan is just that-a fan that slows down when cooling requirements have diminished. This type of fan has seldom been used in North American passenger car applications or Corvettes (cost, size, and complexities being factors). Flexible fans reduce their pitch as engine rpm increases (or more correctly, as pulley speed increases). Fluid coupling fans (sometimes referred to as viscous clutch fans) speed up or slow down-again dependent upon engine or pulley speed. Viscous or "clutch" fans were regular fixtures on Corvettes for years. Electric fans are simply remote units that depend upon the vehicle's electrical system for operation. Dependent upon the application, they can be manually switched or can operate via an integral thermostatic coupling. Of course, late-model Corvettes all came factory-equipped with electric fans.
Horsepower is Horsepower
Certain types of fans require more horsepower for operation than others. Leading the pack in terms of least power absorption is, of course, the electric fan. They rely upon battery power to operate, but keep in mind that the battery will be drained when the unit is in operation. That means the charging system has to keep up (basically, the engine has to power the alternator demands instead of turning the fan, and it still must power the water pump and other accessories). In terms of conventional fans, both the flex fan and the clutch fan offer considerable advantages as far as horsepower losses are concerned. Obviously, a flex fan is far less complicated than its clutch fan stable mate, but it too has some drawbacks. Some flex fan designs simply take a "set" at a given position following sustained use. The result, of course, is too little fan action and, ultimately, reduced cooling. Depending upon the Corvette, one of the safest bets in terms of fans is the original equipment style clutch or fluid coupling system. When the clutch mechanism is in competent operating condition, the fan works flawlessly, declutching as the engine speed or pulley speed increases. The final outcome is more available horsepower when you need it.
When dealing with conventional fans, one area that you should think about is a phenomenon called blade stall. Similar to an aircraft propeller, the fan attached to your Corvette engine can in fact be turned too fast. A massive amount of turbulence is created that effectively decreases the airflow through the radiator. Obviously, overheating will be the consequence, but fixing the problem might be more difficult. The only real solution is to reduce the speed of the fan, which can be handled easily with a pulley that's a different diameter.
This is a very common arrangement...
This is a very common arrangement found on many Corvettes up to the C4 models. It's a viscous or "clutch" fan. This is the fan type that, in most cases, should deliver the best performance in any vintage Corvette. Yes, it's an OEM factory clutch fan. And it's certainly not a trick, sophisticated piece. In operation, the clutch allows the fan to speed up or slow down-again dependent upon engine or pulley speed. Because of this, the fan decouples as engine speed increases, more or less freewheeling at high rpm. Given the freewheeling nature, there's little power loss when the car is accelerating. In contrast, the fan couples up when the engine speed is low. By coincidence (or perhaps more correctly, design) this gives the engine the maximum amount of cooling when it's needed the most.
Take a close look at the fan...
Take a close look at the fan and shroud in this '66 L72 Corvette. Two things are important: There's a shroud in use, and the fan blade tips are actually very close to the edge of the shroud. In effect, this leads all of the available air through the radiator.
Late-model C3 Vettes were...
Late-model C3 Vettes were jammed with hardware. The fan was still crank driven, and obviously, positioned behind the radiator. The trouble here is there is so much stuff inside the engine compartment, there's little room for airflow. This would eventually change as the Corvette matured.
Leading a Horse to Water
With later C4 models, the...
With later C4 models, the cooling fan situation changed dramatically. Engine compartments became much more organized, but the fan arrangement grew in sophistication. For example, 1990 and later Z51- and Z52-equipped cars were factory fitted with a puller and a pusher fan (both of the electric variety).
When it comes to cooling, you absolutely must figure out a way to bring the air to the cooler. The idea is, of course, to provide a constant supply of air through the radiator so that the coolant is reduced in temperature. Increasing the airflow through the radiator improves the cooling and, as a result, a shroud is almost mandatory on high-performance applications. Unfortunately, they're often missing on older Corvettes. Keep in mind the shrouds were often manufactured from plastic and, as a result, the condition typically degrades dramatically over the years. On a similar note, Corvettes that were raced seldom have them (for example, L88 models). If you don't have a shroud or if it fits poorly, get the right one (that's a big hint if you end up sitting behind Old Faithful on a regular basis).
How does the shroud work? Basically, the shroud surrounds or partially surrounds the fan. It butts up tightly to the face of the radiator, effectively sealing the cavity. This isolates the pocket of air behind the radiator, allowing the fan to efficiently draw the required air through the radiator. If the shroud is not present, it creates a considerable amount of dead space behind the radiator that in turn destroys the effectiveness of the fan assembly. The bottom line is simple: If you don't run a proper shroud, you're only asking for overheating grief.
In the case of electric fans, you usually have two options: a pusher fan or a puller fan. Chevrolet has used both configurations in modern passenger cars, Corvettes, and light trucks, although puller fans are the most common. Sometimes electric fans are used in conjunction with an engine-driven clutch fan (typically, an electric pusher fan mounted ahead of the rad). This arrangement is particularly useful if heavy cooling tasks are mandated by the application (a good example is a pickup truck with a factory towing package). This might be a good choice for a Corvette that's either blessed with a cooling dilemma or one that sees double duty as a weekend racer.
So which fan is best for your Corvette? It all depends upon the application and the room you have to work with. If you have the room, a Detroit-style engine-driven clutch fan with a full shroud is most certainly a good bet. Another really good arrangement is a dual electric puller system, complete with an integral shroud (as shown in the accompanying photos). The worst possible arrangement is an inexpensive discount store flex fan without a shroud or a single pusher electric without a shroud (with these setups, you're only asking for trouble). All of the other combinations fall somewhere in between.
When all is said and done, there is one major point to keep in mind: There is virtually no way to "over cool" your Corvette. And the more power your engine produces, the more cooling capacity you'll need. Just some food for thought.
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Today, wrecking yards are...
Today, wrecking yards are full of electric fans. When using these previously owned fans in a Corvette, keep this in mind: The fan can be made to either push or pull, depending upon the polarity of the wiring. Make sure it's right for your car (pusher or puller) or you'll end up chasing a stubborn cooling issue. Additionally, some electric fans can have their orientation or "index" revised. In order to orient the electrical harness plug location on the fan, typically four screws on the fan motor body (called a "cap" by most manufacturers) must be removed and the electric motor re-indexed on the integral fan hosing. This moves the fan wiring harness to the location you need in relation to the vehicle wiring harness. In turn, this provides for neater customized wiring routing.
The darling of corner discount...
The darling of corner discount stores everywhere is the flex fan. Basically, these fans have blades that flatten out at high rpm. Less blade pitch means less power to turn. When buying flex fans, beware of fans with flimsy blades. For example, some aluminum flex fans have a tendency to flatten out with use, and remain that way. The result? A lack of cooling over a period of time. A better idea is the use of a stainless steel blade. It has a better "memory" than its aluminum counterparts, and because of this, has a tendency to flex and then return to its shape on a regular basis. This stainless steel Moroso model uses nicely set rivets with adequate spacing between the rivet holes and between the edges of the central hub. Some cheap look-alike fans don't have this attention to detail. Finally, keep in mind that some flex fans are made from plastic. I've only had experience with them in drag race applications (where they work great), but I suspect you should disregard them for sustained use.
If you're Vette Rodding an...
If you're Vette Rodding an originally small-block-powered '63-'72 Corvette, that OEM Harrison radiator and stock fan setup may not be up to the job of keeping a modern-tech LS engine cool, especially if it's gone volcanic more than once. That's where DeWitt's new LS Series radiators come in. These all-aluminum radiators feature modern-day cooling connections and coolers built right in, while fitting into your Vette's original small-block core support. They're also equipped with a built-in temperature sensor, stem line, plus dual 11-inch Spal fans with ready-to-install wiring.
It's no secret that electric fans are pretty much the norm today, particularly with modified Corvettes or late-model jobs. But there's a catch when it comes to fans: You have to get something with sufficient power to cool the car, but at the same time, get something that doesn't have a ridiculously high amperage draw. This is critical for many cars because of the drain on the charging system. Companies such as Ron Davis Racing Products have spent considerable time researching cooling fans with these criteria. Davis offers a trio of fans-12-inch, 14-inch, and 16-inch diameters. Specs are as follows:
All of the above have a low-amp draw, but Ron points out that one of the other secrets to properly cooling a high-performance car is to effectively seal the radiator to the fan. Typically, this is accomplished by way of an integral shroud surrounding the electric fan (as shown here with this Davis-built radiator). The shroud simply allows the largest volume of air to be pulled through the rad (typically in a pull-through application).