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.
What's Best?
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.