Although winter is firmly upon us, that doesn’t mean our classic rides are removed from our thoughts. This is the time of year we can do some much-needed maintenance or even a few upgrades. If your summer cruising saw your car’s temperature gauge reading higher than you think it should, maybe it’s time to change out that mechanical, factory four-blade air mover for an electric fan. We partnered with SPAL Automotive to dive into design considerations when choosing an upgrade. However, before you begin wrenching, there are a few things you probably should consider.
If you want to add an electric fan setup you need to first figure out what electric fan will work best for your application. For instance, can a puller-style fan fit between your engine and radiator, or do you need a pusher? Fitment is a big issue for many who want to add an electric fan(s).
SPAL has pusher and puller fans as available options. The pusher-style fan mounts on the front of the radiator, and as its name indicates, pushes air through the radiator. Pusher fans are typically installed when there just isn’t enough room to mount the fan between the radiator and engine. A puller fan is by far, the more popular choice. It’s more efficient, because it mounts on the back of the radiator, draws air through, and does not block airflow.
Push Or Pull
“Using a puller fan is seen as a better practice,” says Brent Chuck, application engineer at SPAL USA. “Mounting the fan in front of the radiator adds a restriction to airflow through the system. So, it’s seen as a better practice to put the fan on the engine side and add the restriction after the radiator. When the fan is mounted as a pusher, it becomes more of a restriction to the ‘free air cooling’, or ram airflow through the radiator. Pusher fans are often mounted right against the radiator face, which can create a ‘dead spot’ or an area of low airflow where the motor is mounted on the radiator. Our motors are usually 5-inches in diameter, so you can imagine a 5-inch circle of little or no airflow where the motor lines up on the radiator. Usually, this is fixed with a good shroud or adding an air gap when using the fan as a puller. But using a shroud on a pusher typically isn’t a great idea either.”
Some might argue that a pusher is more efficient because the air the fan is acting on is often cooler and denser than seen by a puller in the engine bay. That might be true, but usually, the benefits of a pusher in colder air don’t out-weigh the con of having the fan mounted in front of the radiator.
Does SPAL recommend using pusher fans? “Yes,” states Brent. “In some cases, where space is tight and it’s the only option. But it’s not really seen as good practice within our industry. It’s like seeing a car with a pusher and a puller fan on the same radiator. Can it work? Yes, but is it ideal? No, absolutely not.”
Taking The Curve Or Going Straight
Another thing to consider is blade design. SPAL has various blade designs to choose from (straight, curved, and paddle), and each has an operational parameter. “Usually, people have the best results from the thicker fans and the thicker fan blades,” says Brent. “I typically recommend fans like our part number 30102082 with a curved-paddle blade. This blade style has a more aggressive blade profile, and it’s able to have a more aggressive blade because the fan is thicker overall. This blade style offers good airflow and pressure performance at lower RPM. So you get a fan that performs well and provides better noise characteristics. Since it is heavier, it takes more current draw (amps) to spin, but performance and noise are usually more important to our customers than using a few extra amps.”
“The curved-blade fan (not to be confused with the curved paddle-blade fan), like part number 30102049, is great for customers that are tight on space,” Brent continues. “When they can’t fit the thicker fans, they need something with a thinner blade. These fans still offer good airflow performance and decent pressure performance. This style makes more of a whining sound because it’s a really lightweight, narrow-blade profile being spun at faster RPM. Some people compare the sound to a supercharger whine or a jet engine. But if you need more performance and space is tight, they can be a great option.”
The straight-blade design like what is found on part number 30100375 creates a fair amount of noise, and many forego this as an option for their classic because of that noise. Straight blade fans are recommended for applications in which noise is not a major issue. On the upside, this fan design delivers strong airflow, mounts in tight spaces, and has a low current draw. While some will tolerate the noise because of the volume of air it pulls through the radiator, others might not be able to live with the noise. “The straight-blade fan is the noisiest, and the curved ‘S’ blade will be a close second,” Brent confirms. “The curved-paddle blade is the best for noise and performance, but it is a thicker fan.”
According to Brent, “unfortunately, with airflow and noise, it boils down to physics, and there’s no such thing as a free lunch. You’re either moving air and making some sort of noise, or you’re not really moving air. Blade profile can change the tone or audible noise heard from the fan. This also ties into dBA ratings. If I give you a dBA rating for a fan, you have an idea of how loud it can be, but you can’t tell if the sound is annoying or displeasing.”
All three fan designs will deliver exceptional cooling in most applications. For most enthusiasts, the ideal fan offers the best efficiency while meeting static pressure load, amp draw, and fan noise requirements. “The curved-paddle blade is the best design in terms of generating pressure, and it provides the best noise characteristics,” Brent states. “The straight blade is the worst in terms of noise, and the curved S-blade is just a compromise on the straight blade in an attempt to reduce the noise. You will lose performance going from the straight blade to the curved S-blade. However, the fan will also be slightly quieter.”
In A Nutshell
- The curved-paddle blade is the best for performance but is a thicker fan requiring more room.
- The straight blade is the next option in regard to performance.
- The curved S-blade does not perform as well as the others.
- The straight-blade fan is the loudest.
- The curved S-blade delivers improved noise reduction.
- A paddle blade is the quietest. The blade design is more aggressive, so it makes more of a wind sound versus a whining sound like the others.
“Basically, we always recommend paddle blades if you can fit them,” says Brent. “They offer the best noise/performance. The other two designs are simply made to be thin, so they make a less desirable noise.”
The Big Blow
Finally, electric fans are rated according to the amount of air that can be pushed or pulled through the radiator. This is measured in cubic-feet-per-minute (cfm). In order to find the fan that will work best for your needs, you first need to determine the ideal amount of airflow required to meet your cooling capacity. As a guideline, a typical small-block uses roughly 2,800 to 3,000 cfm of airflow, while a big-block typically requires 4,500 cfm. Keep in mind, these numbers are just guidelines, and each appl. However, cfm ratings might not be as important as you would think.
“Don’t sweat cfm ratings,” Brent assures. “People get told they need 2,000 or 3,000 cfm from people who don’t know what they’re talking about. CFM ratings are often obtained in free air conditions, which are not the same conditions people expect to use the fans mounted on a radiator. That means that the number doesn’t mean much. It’s something that is good to know, but not something I recommend looking for when selecting a fan. If a fan claims 2,000 cfm, it won’t be 2,000 cfm as soon as you put it on the radiator. Just understand what your radiator stack (radiator, A/C condenser, oil cooler) looks like and understand that each component is adding a restriction to the system. The more restriction you add, the more pressure your fan has to generate to overcome the restriction.
If you have a restrictive cooling stack, look for a fan that generates more pressure. SPAL has tabular airflow data available for all our fans. Look at airflow data, and don’t just look at the highest cfm number. Also, look at how many amps the fan draws, and how much static pressure it can generate. Comparing the tabular data between other fan models, it becomes easier to compare with more data and more apparent as to which models are better for your application. Even if you don’t know the static pressure requirements of your radiator stack, you can still figure out which fans generate more pressure/flow.”
Now that you have some useful information about electric cooling fans, you can upgrade your hot rod so next summer’s cruising doesn’t cause your engine to get a little hot during those cool rides.