Why Your Belt-Driven Fan Is Robbing You of Horsepower

Every internal combustion engine wastes a portion of its output driving ancillary components. One of the biggest thieves is the mechanical, belt-driven cooling fan. Spinning constantly, regardless of engine temperature, it creates significant parasitic drag. For enthusiasts seeking a practical, bolt-on power increase, the Davies Craig Electric Fan Conversion System offers a proven solution: replace the heavy, power-sapping mechanical fan with a lightweight, thermostatically controlled electric unit. Properly executed, this swap can unlock 10 to 15 rear-wheel horsepower while improving cooling efficiency and fuel economy.

Understanding Parasitic Drag and the Davies Craig Solution

Parasitic drag is the energy required to rotate accessories like the alternator, power steering pump, and, notably, the engine cooling fan. A typical mechanical fan can consume 8 to 15 horsepower at highway speeds, and even more during low-speed, high-load conditions. The Davies Craig system eliminates this load entirely. When the engine is cool, the electric fan stays off, meaning zero drag on the crankshaft. When cooling is needed, the fan draws only a fraction of the power that a mechanical fan requires, and only when necessary. This on-demand operation is the key to the power gain.

Davies Craig has engineered its electric fan systems for robust airflow, often exceeding the CFM (cubic feet per minute) of the original mechanical fan, ensuring you don’t sacrifice cooling performance for horsepower. Their design philosophy focuses on high-efficiency motors and aerodynamic blades, making them a top choice for both street and track use. For more on the engineering behind their fans, visit the official Davies Craig website.

Detailed Benefits of Converting to a Davies Craig Electric Fan

1. Measurable Horsepower Gains of 10–15 HP

The headline figure is not marketing hype. By removing the mechanical fan (its clutch assembly, shroud, and heavy blades) and wiring in an electric unit, you reduce rotating mass and parasitic draw. Independent dyno tests on popular V8 and V6 platforms routinely show gains of 10–15 wheel horsepower. On smaller four-cylinder engines, the percentage gain is even more noticeable. For documented results from a real-world install, check out this Hot Rod magazine dyno test of the Davies Craig fan.

2. Improved Fuel Economy

Less load on the engine means less fuel consumed. While the exact gain varies by driving style and vehicle, many owners report a 1–3 MPG improvement, especially in city driving where the engine would otherwise be fighting the constant drag of the mechanical fan. The electric fan only runs when the coolant temperature reaches a set threshold, so it is off much of the time during highway cruising.

3. Superior Cooling Performance

Davies Craig fans are designed with a high-pressure, high-volume airflow curve. They push air through the radiator core more effectively than many OEM fans, particularly at low vehicle speeds where mechanical fans are least efficient. By moving the fan closer to the radiator and sealing the shroud properly, you can lower coolant temperatures by several degrees under sustained load.

4. Noise Reduction

Mechanical fans, especially those with fixed blades, emit a constant roar. The Davies Craig electric fan operates so quietly that you may forget it is running. This makes long highway drives more pleasant and eliminates the “jet engine” sound at idle from some aftermarket mechanical setups.

5. Adjustable Thermostatic Control

Davies Craig systems include a thermostatic controller that allows you to set the fan on/off temperature points independently. This gives you finer control over engine operating temperature, useful for tuning applications or vehicles with higher-compression engines that benefit from a cooler intake charge. You can wire the fan to a manual override switch as well, giving you the ability to pre-cool the radiator before a hard run.

Selecting the Right Davies Craig Fan Kit for Your Vehicle

Davies Craig offers several fan sizes and configurations. The most popular units for street performance are the DB1206 (12-inch, 1600 CFM) and the DB1606 (16-inch, 2100 CFM). For larger radiators or high-horsepower engines, a dual-fan setup using two DB1206 fans can move over 3000 CFM. Consider the following factors when choosing:

  • Radiator core width and height: The fan must cover the core area without blocking airflow. Measure your radiator dimensions.
  • Engine bay clearance: Some vehicles have limited space between the radiator and engine. Davies Craig fans are slim (typically 3 inches thick) but always measure your available depth.
  • Amperage draw: Ensure your charging system can handle the load. A single 16-inch fan typically draws 12–18 amps; a dual setup draws up to 35 amps. Upgrading the alternator or adding a relay is often recommended.
  • Controller type: Davies Craig offers fixed-temperature switches and adjustable controllers. The adjustable unit (e.g., part #0677) provides the most flexibility.

Comprehensive Installation Guide for Davies Craig Electric Fan

Below is a detailed step-by-step process for a typical installation. Always consult the specific instructions included with your kit, as variations exist between vehicle models.

Preparation and Tools

  • Davies Craig fan kit with shroud, mounting brackets, and wiring harness
  • Adjustable temperature controller (if not included)
  • Basic hand tools: socket set, screwdrivers, wire strippers/crimpers, Multimeter
  • Electrical supplies: 12-gauge automotive wire, ring terminals, butt connectors, 40-amp relay, fuse holder with 30-amp fuse, heat shrink tubing
  • Zip ties or cable ties for routing wires
  • Drill with bits (if custom mounting is required)
  • Safety glasses and gloves

Step 1: Disconnect the Battery

Remove the negative terminal from the battery and secure it away from the terminal post. This prevents accidental shorts and protects the ECU.

Step 2: Remove the Old Mechanical Fan and Shroud

Depending on your vehicle, you may need to remove the radiator shroud first (which is often secured with plastic rivets or screws). Then use a fan clutch wrench or a large crescent wrench to remove the fan blade assembly from the water pump hub. Be careful—the threads are typically reversed. Once the fan is off, remove the fan clutch (if separate) from the water pump. Double-check that all bolts are accounted for and set aside.

Step 3: Install the Davies Craig Fan and Shroud

Position the Davies Craig fan assembly over the back of the radiator (engine side). The shroud should seal against the radiator core. Most mounting kits use long bolts that pass through the radiator fins and are secured with rubber grommets and washers. Ensure the fan is centered on the core. Tighten evenly to avoid warping the radiator. For added security, some enthusiasts fabricate bracket adapters—available from Davies Craig for popular vehicles.

Step 4: Wiring the Fan and Controller

This is the most critical part. Follow the wiring diagram provided by Davies Craig. A typical circuit includes:

  • Power feed: Connect a 40-amp relay’s power input to the battery positive terminal through a 30-amp inline fuse. Keep the wire as short as possible.
  • Relay activation: Connect a small-gauge wire from the relay’s control terminal to a switched 12V source (ignition-on) or the fan controller output. Many use the ignition wire from the fuse box.
  • Fan ground: Ground the fan motor to a clean chassis point near the radiator.
  • Controller wiring: If using the adjustable controller, its temperature probe must be inserted into the coolant stream. Davies Craig provides a hose adapter that sandwiches between the radiator top hose and the engine. Alternatively, you can install a threaded bung in the intake manifold or thermostat housing. Run the probe wiring away from spark plug wires to avoid electrical interference.

For a detailed wiring schematic, refer to the Davies Craig official wiring diagrams page.

Step 5: Set Up the Thermostatic Controller

Davies Craig’s digital controller (part #0677) allows you to set the fan on temperature (typically 185–190°F) and the fan off temperature (approximately 10°F lower). Use the included LED display to confirm your settings. Some users wire a manual override switch so they can force the fan on at any time—useful for post-run cooldown or stop-and-go traffic.

Step 6: Reconnect the Battery and Test

Reconnect the battery. Start the engine and let it reach operating temperature. Watch the electric fan: it should turn on when the coolant passes your set point and turn off once the temperature drops. You can simulate this by grounding the probe to trip the relay manually if you have a multimeter. Listen for unusual noises; the fan should spin smoothly. Check for coolant leaks at the hose adapter or probe bung.

Step 7: Final Checks and Cleanup

Secure all wiring with zip ties away from moving parts and hot surfaces (exhaust manifolds). Test drive the vehicle and monitor the temperature gauge. Verify that the fan cycles on and off as expected. After a few heat cycles, re-tighten any mounting hardware.

Real-World Performance Results

Enthusiasts consistently report a noticeable seat-of-the-pants improvement after the conversion. The engine feels snappier, especially when pulling away from a stop or accelerating from low RPM. On the dyno, the power gain is linear—everywhere in the rev range, you’re not fighting the fan. Beyond the horsepower increase, the engine runs cooler at idle and in traffic because the Davies Craig fan moves air effectively even with no vehicle speed. This is a major advantage for vehicles equipped with large radiators or those used for towing.

In track applications, drivers appreciate the adjustable temperature control. They can set the fan to come on earlier, keeping water temperatures lower before entering a hot lap. The lightweight fan assembly also reduces unsprung weight (when mounted to the radiator, which is attached to the chassis) by several pounds compared to a mechanical fan setup with its heavy steel clutch.

Maintenance and Troubleshooting

Electric fan systems require minimal upkeep. Periodically inspect the fan blades for debris or damage. Check electrical connections for corrosion, especially if you drive in wet conditions. The biggest failure point is the relay—always carry a spare 40-amp relay in your glove box. If the fan fails to operate, use a multimeter to test power at the relay and continuity through the thermostat probe.

One common issue is the fan running continuously. This usually indicates a faulty temperature probe or a shorted wire. Ensure the probe is not touching the engine block directly, which can give false high readings. Conversely, if the fan never turns on, the most likely culprit is a blown fuse or a faulty thermostat controller.

Conclusion: The Smartest 15 Horsepower You’ll Ever Buy

Investing in a Davies Craig Electric Fan Conversion System delivers a compelling combination of power, efficiency, and cooling control. The 10–15 horsepower gain is real and repeatable, and the installation is well within the reach of a competent DIY mechanic. By shedding the parasitic drag of the belt-driven fan, you reclaim engine output that was always there but wasted. Combined with better fuel economy, quieter operation, and adjustable thermal management, this upgrade remains one of the best value-for-money performance modifications available. Choose the correct fan for your application, follow the wiring guidelines carefully, and enjoy the immediate benefits of a more responsive, cooler-running engine.