What is "SDI" on a Ski-Doo?

The term SDI on Ski-Doo snowmobiles stands for semi-direct injection. This SDI technology was developed as a way to create a two-stroke engine that is more efficient and more powerful.

Ski-Doo developed their SDI technology in part due to the United States Environmental Protection Agency putting stricter standards in place on the emissions from small engines such as those found in snowmobiles. While other snowmobile manufacturers chose to do away with two-stroke engines altogether in favor of less polluting four-stroke engines, Ski-Doo instead chose to develop new technology that would allow two-stroke engines to be much cleaner burning, with the result being semi-direct injection.