The highest capacity engine used on motorcycles can vary depending on the specific context and purpose of the motorcycle. There have been motorcycles with extremely large engines designed for various purposes, including record-breaking speed, heavy-duty touring, or specialized applications. Here are a few examples:
Dodge Tomahawk: Although not a conventional motorcycle, the Dodge Tomahawk was a concept vehicle that featured a 8.3-liter V10 engine sourced from a Dodge Viper sports car. It was a four-wheel vehicle with two wheels placed in the front and two in the rear, but it was designed to look like a motorcycle. The engine had a capacity of 8,277 cc (505 cubic inches).
Boss Hoss motorcycles: Boss Hoss is a motorcycle company that specializes in producing large-displacement motorcycles. They have manufactured bikes powered by V8 engines borrowed from automobiles, with capacities ranging from 5.7 liters (350 cubic inches) to 8.2 liters (502 cubic inches).
Harley-Davidson Screamin' Eagle Milwaukee-Eight: In the realm of production motorcycles, the Harley-Davidson Screamin' Eagle Milwaukee-Eight engine stands out with a displacement of 1,868 cc (114 cubic inches). It is used in Harley-Davidson's high-performance models and offers significant power and torque.
It's important to note that engine capacity alone does not determine a motorcycle's overall performance or desirability. Factors such as engine design, efficiency, weight, and other performance characteristics also play crucial roles in a motorcycle's performance.