Harley-Davidson, the iconic American motorcycle manufacturer, has been known for its classic air-cooled engines for decades. However, in recent years, the company has embraced liquid-cooled technology in some of its newer models, offering a blend of traditional design and modern performance.
The Transition to Liquid Cooling
In 2014, Harley-Davidson introduced liquid-cooled cylinder heads for several of their models, including the Touring and Softail lineups. This hybrid cooling system featured an air-cooled engine block, with the coolant focusing on the exhaust valves to improve thermal management and performance.
The key benefits of this liquid-cooled system included:
- Improved Thermal Management: The liquid cooling system helped dissipate heat more efficiently, particularly in high-performance or high-load situations, such as long-distance riding or towing.
- Enhanced Durability: By targeting the exhaust valves, the liquid cooling system helped extend the lifespan of critical engine components, reducing the risk of overheating and premature wear.
- Increased Power Output: The improved thermal management allowed for higher compression ratios and more advanced ignition timing, resulting in a slight increase in power output.
The Revolution Max Engine
In 2020, Harley-Davidson took a more significant step towards liquid cooling with the introduction of the Revolution Max engine. This all-new V-Twin powerplant, found in the Pan America and Bronx Streetfighter models, features a fully liquid-cooled design.
The Revolution Max engine boasts the following technical specifications:
- Displacement: 975cc or 1,250cc
- Cylinder Configuration: 60-degree V-Twin
- Cooling System: Liquid-cooled with water pump and thermostat
- Valvetrain: DOHC, 4 valves per cylinder
- Compression Ratio: 13.0:1 (975cc) or 13.2:1 (1,250cc)
- Peak Power: 150 hp (112 kW) at 9,000 rpm (975cc) or 150 hp (112 kW) at 8,750 rpm (1,250cc)
- Peak Torque: 94 lb-ft (127 Nm) at 6,750 rpm (975cc) or 94 lb-ft (127 Nm) at 6,750 rpm (1,250cc)
The fully liquid-cooled design of the Revolution Max engine allows for improved thermal management, increased power output, and enhanced reliability, making it a significant departure from Harley-Davidson’s traditional air-cooled powerplants.
Liquid-Cooled Models in the Lineup
In addition to the Pan America and Bronx Streetfighter, Harley-Davidson has introduced several other models featuring liquid-cooled engines:
- Sportster S: Powered by the Revolution Max 1250T engine, the Sportster S also benefits from liquid cooling for improved performance and efficiency.
- Custom Vehicle Operations (CVO) Models: Some of Harley-Davidson’s high-end CVO models, such as the CVO Street Glide and CVO Road Glide, come equipped with liquid-cooled engines.
- 2023 Models: Select 2023 Harley-Davidson models, including the Pan America™ 1250 Special, Nightster®, Nightster® Special, and Sportster® S, feature the liquid-cooled Revolution® Max 975 engine.
Maintaining the Air-Cooled Legacy
While Harley-Davidson has embraced liquid-cooled technology in some of its models, the company has also taken steps to preserve the classic air-cooled engine design. One such example is the introduction of the Variable Valve Timing (VVT) system, which helps the air-cooled engines stay in production for a while longer by improving their performance and efficiency.
The VVT system works by adjusting the timing of the intake and exhaust valves based on engine speed and load, allowing the air-cooled engines to maintain their distinctive character while also benefiting from improved power delivery and fuel efficiency.
Conclusion
Harley-Davidson’s transition to liquid-cooled engines represents a significant evolution in the company’s design and engineering approach. By blending traditional air-cooled technology with modern liquid-cooling systems, Harley-Davidson has been able to offer a range of motorcycles that cater to the diverse needs and preferences of its customers, from classic enthusiasts to performance-oriented riders.
As the motorcycle industry continues to evolve, it will be interesting to see how Harley-Davidson navigates the balance between preserving its iconic air-cooled heritage and embracing the performance and efficiency benefits of liquid-cooled technology.