The secrets of the new Harley-Davidson Revolution Max engine

If you're a motorcycle enthusiast, you've probably heard about the launch of Harley-Davidson's first "Adventure" model, streamed as a world premiere: the Pan America 1250.

This model marks a very important milestone in the brand's history, as it incorporates the powerplant that will be used in most new models in the coming years: the Revolution Max engine.

This engine was designed from the ground up, unrestricted by any particular chassis or model, allowing engineers the freedom to innovate its features. This freedom, of course, is limited to:

• Comply with emissions regulations in different markets.
• Create a product that is competitive in price and performance.
• Staying within a budget determined by the competition.
• Obtain an attractive product for current and new customers of the brand.

Let's review the most distinctive features of this engine, both compared to other Harley-Davidson models and similar options from the competition.

Liquid cooling

To comply with emissions regulations, temperatures must be controlled. High temperatures require more fuel to cool the cylinder walls and, at the same time, generate polluting gases and toxic particles. Liquid-cooled engines pass this fluid through the hottest areas, removing heat from the surfaces and lowering their temperature. The water then passes through a forced-ventilation radiator, which transmits some of this heat to the outside, cooling the liquid again. The water jackets insulate the engine sound, allowing the manufacturer to allocate more decibels to the exhaust, within the law.

Aside from emissions issues, having temperature control in an engine means less component expansion, tighter tolerances, and increased power and longevity. All this comes at the cost of increased engine design and maintenance complexity.

Double overhead camshaft

The DOHC system has been used in automobiles since 1910. Dual Overhead Camshaft means the valves are actuated directly by the camshafts, which are located above them, with one camshaft for intake and one for exhaust. Pushrods and rocker arms are therefore eliminated (reduced to a minimum).

The main advantage is that we're eliminating components that generate a lot of inertia (due to their weight) and imprecision (due to torque), which means the engine can be revved faster and to a higher RPM without damaging it. DOHC engines require expensive and complex valve clearance maintenance (if you've ever tried to do it on a V-Rod, you know what I'm talking about). But this engine is Harley and has to be different, so hydraulic tappets are used, which eliminates valve timing.

Variable distribution

Perhaps the most important new feature of this engine, which also differentiates it from many of the competition, lies in the VVT (Variable Valve Timing) system.

In a very simplified way, we can say that this system is based on an electric motor that is capable of varying the position of each camshaft at all times, so it is as if instead of a fixed camshaft, we were able to change the camshaft for a different one, in real time.

To understand the advantage this offers, it's necessary to understand how the camshaft works. It's not just an element that provides more or less power; it simply determines where maximum torque is delivered, defining the engine's "character." We can install a "touring" camshaft in the same engine, which offers plenty of low-end and endless torque, resulting in a smooth, easy-to-ride, and powerful bike. On the other hand, installing a "sport" camshaft results in a more playful and aggressive engine, requiring shifting at high RPMs to maintain power.

Well, VVT offers us the best of both worlds, or of 3, 4, or infinite, since it is capable of modifying the angle of attack of the opening and closing of valves so that we obtain the ideal behavior at any given speed, improving starting, emissions control, traction control, etc. As with the technologies mentioned above, this adds greater complexity, both in maintenance and programming, since the camshaft must be "mapped" according to the rest of the engine management maps.

Other technical characteristics

• Harley-Davidson's Revolution Max engine is a 60-degree twin-cylinder engine with a displacement of 1250cc and 150 hp at 9000 RPM.
• This engine is a component that withstands external stress , meaning it works as part of the chassis, providing rigidity, thus allowing for smaller and lighter chassis. The center of gravity has been kept as low as possible to provide stability both while moving and stationary.

• The engine covers (clutch, alternator, and camshafts) are made of magnesium, a high-tech detail, as they weigh only two-thirds of their aluminum counterparts.
• We have 5 different driving modes and cruise control.
• Exhaust valves filled with sodium, which cools them in a process similar to human sweat: it evaporates, eliminating heat, and turns into droplets that slide down the valve to begin the cycle again.
• Crankshaft balancing . Interestingly, the crankshaft and counterbalance shafts allow for perfect balance, virtually reducing vibration. However, they have been deliberately "incorrectly" configured so that users (especially those from the brand's traditional sector) don't lose that powerful engine feel.
• Engine block design . In this type of engine, the cylinders are generally part of the engine block. In true Harley-Davidson tradition, these cylinders are removable, allowing for the installation of Big Bore kits and, possibly, smaller cylinders if mid-displacement models are developed in the future. The cylinder heads feature dual spark plugs to improve combustion efficiency.
• Lubrication system. In this case, Harley-Davidson applies techniques derived from racing to achieve a high-performance lubrication system, consisting of injecting oil from the end of the crankshaft (as it had done with Big Twin engines) and driven by three independent oil pumps (center, right side, and left side). This reduces internal crankcase pressure and improves piston efficiency, similar to racing engines (again, another technique inherited from dry-sump Big Twin engines).

Apart from the engine

The electronic management system of such an advanced engine also allows the use of resources (control units, sensors and actuators) to offer advanced functionalities, already available in the Pan America 1250 model:

• Adaptive Height System , the first of its kind on any production motorcycle on the market. When the motorcycle detects a stop, it lowers its height so the rider can comfortably lean back, raising it again based on speed.
• Semi-active suspension . Long loyal to the Showa brand, the Motor Company's engineers have developed control software for both suspensions, which varies the suspension's behavior based on the bike's usage via the ECM (the bike's main computer, which also controls engine management). The rear shock absorber incorporates the BFRT (Balance Free Rear Cushion) control system derived from racing bikes.

• Hill Start Assist . This is a Hill Holder system that, with the help of the ABS brakes and traction control system, makes it easier to start from a standstill on a hill.
• Improved cornering control . With the help of an IMU (Inertial Measurement Unit), the bike's computer will help us maintain the line while cornering, controlling engine torque, braking, and suspension. As if by magic, it will seem like our riding skills have improved.

Conclusion

Before us is the engine that will likely power the next generation of Sportster models and which could be the brand's last bastion of internal combustion engines before electric models monopolize the market.

It's a powerful, modern engine that will have to win the loyalty of current Harley-Davidson motorcycle owners with its reliability and also be able to attract customers from other brands, a real challenge.

Frank Burguera

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