Choosing the right fan is critical for achieving the right level of cooling for your vehicle. Whether you’re trying to cool a street car or a race car, you need the best solution for your specific configuration. We had the opportunity to ask our friends at SPAL USA some in-depth questions about choosing a fan and the different types of fans available on the market.

Selection and Compatibility of Cooling Fans

1. What should I look for in choosing a fan for a street car, and how is that different from what is needed for a race car?

Choosing the right fan is largely based upon the vehicle the fan is going into and the cooling required. The first step to choosing a fan is looking at the power available to run the fan. How big is the alternator, and how many Amps are available to power the fan? It is important to note that the SPAL fan could potentially be the largest continuously powered electrical device on the vehicle and to make sure the fan chosen does not excessively drain the battery by drawing more power than the alternator can keep up with.

Once you know what power draw the battery and alternator can support, look at the available space in the vehicle. If the radiator is only 14 inches wide, it becomes very hard to attach a 16-inch fan. If the radiator is 26 inches wide and there is a pulley right behind the radiator in the center, we generally find it more ideal to put two 12-inch fans side by side to avoid the pulley system and fit in the space we have available.

Once the vehicle is understood with power and space available, we look at our fan options. The fan performance is determined by the power of the motor and the air pressure the fan is designed to work at. The air pressure of the cooling system is directly related to the radiator; the thicker the radiator or the tighter packed the fins are, the higher the pressure.

A typical automotive radiator 1-2.5 inches in depth is generally in the range of 100-300 Pascals. If the exact pressure is unknown, SPAL’s general recommendation is to go for the largest, most powerful fan that your system can support with some control structure to turn the fan on and off when it is needed and not needed. It is common above a certain vehicle speed the fan generally does not even need to turn on and the passive airflow caused by driving is enough to effectively cool the engine. This speed is generally roughly between 45-60 mph.

The most powerful fans are all going to be brushless. While the brushless fans offer many benefits, this is perhaps the greatest for keeping your vehicle cool when you really need the best performance. For most vehicles, SPAL brushless fans are the ideal solution.

When looking at other options, the more classic brushed style fans can, however, be a better fit for some vehicles if things like space become tight. The brushed fans have a thinner blade profile with the depth of the fan being determined by the motor, sticking out of the fan only in the center few inches.

It is important to note that while SPAL offers 4 different motor depths with brushed fans, the power of the fan (and therefore its cooling capability) is directly related to the depth of the motor. The bigger (deeper) the motor, the more power the fan provides to cool your vehicle. This is sometimes where choosing the right fan can create a dilemma. Finding the biggest and most powerful fan requires the most space.

The brushless fans have more limited options, so it is common that either it will fit and work or it won’t. With the brushed fans, if the vehicle only has 2.7 inches of space behind the radiator, the High Performance series (3.45-inch motor depth) fans will not fit, while the Medium Profile fans (2.44-inch motor depth) will fit well. In this scenario, balancing the brushed vs brushless fan as well the motor power is the result of these multiple factors.

For all 12 Volt race car vehicles, the same advice would hold true with the additional consideration of the brushless startup time. SPAL brushless fans are electronically controlled to eliminate the startup inrush. This feature helps to protect the vehicle’s electrical system, however, it increases the time required for the fan to reach full speed. Most brushless fans are in the range of 10-15 seconds to go from 0 rpm to full speed.

The brushed fans do not have this computer-controlled limitation on startup time, meaning they will reach full speed in only a couple seconds, with the downside being they have a startup inrush, an initial increased Amp draw on fan startup. In this scenario, the performance is required immediately. Brushed fans can be a great solution.

Another consideration for race cars is for those running on elevated Voltage systems (i.e. 16V, etc.), the brushless fans are digitally monitoring Voltage and will shut down at 16V to self-protect the motor. This makes brushless fans largely non-functional on 16V systems.

While the official SPAL operating conditions for brushed fans are 12V ±10% (11.8-13.2V), brushed fans operate on the mechanical principle that if the fan sees power the fan will run until it won’t (this is the reason the fuse is so important as it is the only safety protection for the vehicle with brushed fans). With a brushed fan motor design, the motor power will increase exponentially as the Voltage provided increases linearly.

Understanding this, it is generally better and safer to operate the SPAL Low or Medium Profile fan series vs the High Performance Series if you are selecting a fan for a higher Voltage system. It also must be understood that the lifetime of the fan is reduced (more dramatically the further away from 12V you are) when operating outside of the SPAL operating conditions.

SPAL brushless fan assembly

Brushed vs. Brushless Cooling Fans

2. What is the difference between brushed and brushless cooling fans, and why choose one over the other?

The main difference between a brushed and a brushless electric motor cooling fan lies in the motor design and how they operate. Here’s a breakdown:

 Brushed Electric Motor Fan:

• Motor Type: Uses brushes and a commutator to transfer electrical current to the motor’s windings.
• Brushes: Brushes make physical contact with a rotating commutator to allow current to flow to the rotor (the part that spins). This generates the magnetic field that makes the rotor turn.
• Efficiency: Less efficient than brushless motors because the friction between the brushes and the commutator results in energy loss and heat.
• Noise: Tends to be noisier due to the friction of the brushes and commutator.
• Cost: Typically a cheaper production cost which results in a more affordable MSRP.
• Durability: Generally, it has a shorter lifespan because of wear and tear on the brushes.

SPAL brushed axial cooling fan

Brushless Electric Motor Fan:

• Motor Type: No brushes or commutator. Instead, the rotor is magnetized and interacts with the stator’s coils that are energized electronically.
• Brushless Design: Uses a more complex controller (electronic speed controller or ESC) to manage the timing and flow of current to the stator windings.
• Efficiency: It is more efficient than brushed motors as there’s no energy lost to friction from brushes. This results in less heat and better performance.
• Noise: Quieter because there’s no friction from brushes or a commutator.
• Cost: Typically more expensive due to the advanced technology and design.
• Durability: A longer lifespan because of the absence of brushes, which wear out over time.

Spal brushless axial cooling fan

Key Differences:

• Brushless motors are more efficient, quieter, and require less maintenance, but they tend to be more expensive.
• Brushed motors are cheaper but less efficient and require more maintenance, with a shorter lifespan.

In summary, if you’re looking for a fan with better performance, quieter operation, and longer life, a brushless fan is the way to go. However, if cost is a major concern and you don’t mind some additional maintenance, a brushed fan could be a viable option.

Sound testing a Spal fan

Determining Efficiency

What size electric cooling fan do I need for my radiator?

Depending on your specific vehicle and application type, we typically recommend whatever size fan will give you the most core coverage. Also, never underestimate the value of a good shroud design in your fan setup.

How do I determine the right CFM (Cubic Feet per Minute) rating for my engine’s cooling needs?

To determine the right CFM (Cubic Feet per Minute) rating for your engine’s cooling needs, you’ll need to consider several factors related to your engine’s size, cooling system, and airflow requirements. Here’s how you can approach the calculation:

1. Engine Size:
The displacement of your engine is one of the main factors in determining cooling requirements. Larger engines typically generate more heat and thus require more airflow to maintain proper temperature.
Formula: CFM = (Engine Displacement in cubic inches) × (RPM / 2,000)
Example: For a 350 cubic inch engine running at 6,000 RPM: CFM=350×6,000/2,000=1,050 CFM

2. Airflow Efficiency:
This depends on the type of engine and its intended use (e.g., street, race, off-road). High-performance or race engines might require additional airflow due to higher power output and heat production.
Street/Stock Engines: May need airflow around 1,000–1,500 CFM.
Performance/Race Engines: May need 2,000–3,000 CFM or more, depending on the modifications and operating conditions.

3. Radiator Efficiency:
The cooling system (radiator, fans, and ducts) plays a role in how much airflow is needed to keep the engine at the desired temperature. A larger, more efficient radiator might lower the required CFM, while a smaller or less efficient radiator might require more airflow to maintain temperatures.

4. Fan Configuration and Cooling Components:

• Electric Fans: The CFM rating of electric fans typically ranges between 500 and 3,500 CFM. If you’re using electric fans, you want to choose fans that meet or exceed the cooling needs derived from the engine and airflow calculation.
• Mechanical Fans: These can vary greatly in terms of CFM. A good rule of thumb is to aim for 1.5–2.5 times the engine displacement in CFM for most standard applications.

5. Additional Factors:

• Ambient Temperature: If you’re in a hot climate, you may need additional cooling.
• Vehicle Speed: Faster-moving vehicles get more natural airflow, which reduces the need for high CFM.
• Air Ducting: The configuration and cleanliness of the air ducts can either help or hinder airflow, so make sure they’re designed efficiently.

Should I use a single or dual electric fan setup?

Similar to the answer for “what size fan do I need for my radiator”, we typically recommend whatever will give you the most core coverage and airflow. Sometimes, staggering two single fans will give you more airflow than a single, larger fan.

How do I ensure the cooling fan fits my radiator and engine bay dimensions?

At SPAL, we pride ourselves on our technical expertise and great customer service. We always recommend contacting our sales team to help determine the correct fan for your specific application.

As you can tell, there’s a lot that goes into making a decision on the cooling fan for your vehicle. We appreciate Spal giving us the insight to get started. Next time, we’ll look at choosing a cooling fan for performance applications.