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Ski-Doo 3-D RAVE exhaust operationRAVE exhaust valves, which debuted on Ski-Doo snowmobiles in the late 1980s, enabled riders to have "two engines in one," one with small exhaust ports for idling and cruising (RAVE closed) and one with large exhaust ports for higher performance and top-end speeds (RAVE valve opened). While the original RAVE valves were opened with exhaust pressure and timing determined by the valve's spring pressure, today's 800 2-TEC Ski-Doo engines use crankcase pressure for the opening force and the ECM and solenoids for the timing. 3-D RAVE adds an intermediate opening position for better performance and fuel economy at the speeds most people ride, about 25-60 mph/40-100 km/h. Engineers accomplished this by splitting the single valve/guillotine into two. When the engine is off, the primary guillotine is closed and the secondary one, including side ports, is open. At idle and at low speeds, a vacuum of crankcase pressure sucks the secondary valve closed. Then, at mid-range engine speeds, the ECM opens the secondary valve to its neutral position by releasing the vacuum. Then at higher speeds, the ECM orders crankcase pressure to push open the primary valve.