2004 Ski-Doo Racing Handbook, Page 143Get this manual
SECTION 05DRIVE SYSTEM
Some 2004 models come equipped with TRA III style drive clutchThey include most models with the 600 and 800 cc enginesThis style of clutch is the "next" generation of engineering development from Ski-Doo and will certainly be used in more models as years go onVisual comparisons between the TRA and TRA III styles may appear slight, but in fact, there are many differences, and when you are working with it, you need to be aware of the differences
The TRA III has Variable Sheeve Angle (VSA)The machined angle of both sheeves varies from 12 degrees at the bottom to 14 degrees at the topThis provides better efficiency through out the entire range of shiftWith the improved efficiency, belt life is also extendedThe TRA III clutch must be matched with VSA type driven clutch and belt to achieve maximum performance