9R ROCK SOLID performance gains! With +3 horsepower on the peak and an astonishing 4-8 additional horsepower in the midrange, the new SLP Power Dome™ head set utilizes our latest combustion chamber design to make this engine consistent, extremely responsive and very rideable. Made from billet aluminum for a durable and dependable design with interchangeable combustion chambers for ease of service. Compatible with 91 octane fuel.