BOMBARDIER 1996 Ski-doo MX Z440 Handbook page 126

To the outside of the return spring is a red plastic adjustment knob (item 5). Turning the
adjustment in or out changes the preload on the return spring which, in turn, will change the RPM
at which the RAVE valve opens and closes. The exhaust port height changes a total of 4 mm to 6
mm (depending on engine type) from the RAVE valve fully closed to fully open.
B) OPERATION
The RAVE valve does not allow an engine to make higher peak horsepower than an engine not so
equipped, it can make moving the peak higher practical because of its effect on the rest of the
power curve. Item 2 in following illustration is the power curve of an engine with the RAVE valve
held fully open through its entire RPM range. Item 6 notes the peak power produced. That peak will
not change if the exhaust port time of a similar engine without a RAVE valve was the same (with all
other features equal).
, A18C02S
Item 1 is the power curve of the engine with the RAVE closed through its entire RPM range. The
shaded area (item 3) is the improvement in power at lower engine speeds that is gained because of
the lower exhaust port. If the port remains at this height, however, the power would peak as noted
in item 5. Raising the exhaust port at the proper RPM (item 7) will allow the engines peak power to
continue to rise to item 6.
Item PI in the illustration is the pressure of the return spring against the diaphragm. The exhaust
pressure must be high enough to overcome this pressure before the valve begins opening. Item P2
is the pressure required to completely open the RAVE valve. Between PI and P2, the useable
power curve of the engine is moving from power curve 1 to power curve 2. This transition takes
place very rapidly at full throttle and from a practical standpoint can be considered to be
instantaneous at item 7 which for the type 583 engine is at 6300-6400 RPM. Gradual application of
the throttle, however, will result in the RAVE valve opening much later, i.e. 7300-7500 RPM.
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