Chaincase Gearing - BOMBARDIER 1996 Ski-doo MX Z440 Handbook

Contrary to popular belief, small gear changes do not directly affect top speed as long as the
clutches are functioning properly. Gearing one or two teeth taller on the top will not generally
make the vehicle any faster on top end unless the clutches are fully shifted out and the engine is
starting to overrev.
With the TRA clutch, we have about 20 percent more shift ratio available compared to previous
designs. Because of this, we have been able to lower the gearing in our chaincase considerably.
For example: '85 Plus square shaft = 26/38 gearing; '86 Plus with TRA = 20/38. Yet, we still have the
same overall top gear ratio because of the 0.8:1 top ratio of the TRA clutch.
This gives us better belt life by allowing our clutches to "slip" for a shorter period of time at
engagement. It also provides more torque to the drive axle for acceleration.
Most snowmobiles are geared on the "high" side from the factory. They are usually geared for 8-
16 km (5-10 MPH) more than they would reach in average conditions. Because of this, the belt does
not seem to go all the way to the top of the drive clutch. This is a normal situation. Snowmobiles
run under widely varying conditions. If all snowmobiles were geared to attain a full shift under
average conditions and then the vehicle were run on a perfectly smooth frozen suface, it would
easily shift out to its geared top speed. Since the drag is so low under these conditions, the engine
would begin to over-rev, eventually lose power, possibly damage the engine, and you will not
achieve top speed.
There are other factors involved here also. As clutches shift through their range, the efficiency with
which they transmit power decreases as the clutch ratio exceeds about 1.5:1. Efficiency also drops
as belt speed (RPM) increases. For optimum chaincase performance ensure that you use the
synthetic chain case oil.
Section 05 TRANSMISSION SYSTEM
05-39