This was Ski Doo's first atempt at a twin engine speed run sled. Here is a little more info on the 600 rotax: In December of 1967, Ski-Doo distributors received a bulletin regarding the Rotax 600cc engine. The bulletin stated that in the near future a limited number of Rotax 600cc engines will be available. It also stated that it was very important that the gear ratio be set up so that the 600cc engine would not turn higher than 6000 rpm's. Under no circumstances should the engine be allowed to rev. up to more than 7000 rpm's. Even if 6000 rpm's seems conservative, if you consider the actual torque curve of the 600 cc there would be no need to set the speed higher than 6000 rpm's. At first it was thought that they would just receive the engine and would install it in the chassis of there choice. The 600cc vertical twin was the first engine Rotax designed especially for Ski-Doo.

This Ski-Doo Double Eagle and is powered by two Fan cooled 399 Rotax twin cylinder engines. 24 of these where built at the factory race shop.

The X-2R is powered by two Rotax 776cc free air twins. The X-2R achived 111.54 mph during the 1971 season, but the following year Yvon Duhamel drove the X-2R to a two run average of 127.3mph. It was finally a world's record for Ski Doo, one that held up for many years to follow.

The Inferno is powered by two Rotax 797 cc free air triples similar to the X-2R but this machine was quite a different beast. Where the X-2R's twin engines were linked to the front drive axle like a conventional sled, the Inferno drove both the front and rear axles, driving the single track from both ends. This was likely the cause for the insurmountable track reliability problems the Inferno suffered. Despite summer time testing that indicated 140mph+ speeds on snow the Inferno disintegrated tracks at speeds in excess of 100 mph. This would be the last factory sponsored speed sled produced by Ski-Doo.