Bombardier SeaDoo 1999 factory shop manual, Page 97Get this manual
Section 04 ENGINE Subsection 05 (TOP END)
787 and 947 Engines 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 horsepower higher practical because of its effect on the rest of the power curveItem in the following figure is the power curve of an engine with the RAVE valve held fully open through its entire RPM rangeItem notes the peak power producedThat peak will not change if the exhaust port time of similar engine without RAVE valve was the same (with all other features equal)Item is the power curve of the engine with the RAVE valve closed through its entire RPM rangeThe shaded area (item 3) is the improvement in power at lower engine speeds that is gained because of the lower exhaust portIf the port remains at this height, however, the power would peak as noted in item 5Raising the exhaust port at the proper RPM (item 7) will allow the engine peak power to continue to rise (item 6)Item P1 in figure is the force of the return spring against the diaphragmThe exhaust pressure must be high enough to overcome this force before the valve begins openingItem P2 is the pressure required to completely open the RAVE valveBetween P1 and P2, the usable power curve of the engine is moving from power curve to power curve 2This transition takes place very rapidly at full throttle and from practical standpoint can be considered to be instantaneous at item 7Gradual application of the throttle, however, will result in the RAVE valve opening much laterP1 P2 6