two strokes

This allows oil ratios from 300:1 at idle to 50:1 at wide-open throttle as performance characteristics require. The good news, according to Mike, is that Brunswick/Mercury formed a subsidiary called MotoTron, which will sell the technology to non-competing industries. This means that many of the snowmobile companies could make a quick phone call to Mercury and inquire about the engine management system from MotoTron.

As we mentioned before, snowmobile emissions standards have not yet been finalized, and it is doubtful that they need to be as stringent as the outboard requirements. Ski-Doo is introducing a simple but very effective system with their Semi Direct Injection (SDI). This system is available this year on the 800 twin engine in the Legend SE. Semi Direct means that the fuel is not injected into the cylinder, but into the rear transfer ports. As a result, the front transfer passages closest to the exhaust port only pumps fresh air.

This is the air source most likely to escape out of the exhaust port. The automotive style injectors pump against the air-stream and are timed against RPM and load to inject fuel just in time to reach the combustion chamber, but not escape out of the exhaust port.

The two injectors are also staged. One injector works all the time, while the other comes in between 3000 and 5000 RPM depending on load. This makes it possible to control the low RPM emissions very closely. The automotive style injectors operate at normal (56PSI) pressure. The ECU is controlled by the RPM, throttle position, air temperature, barometric pressure, water temperature and manifold pressure input. The inclusion of a manifold pressure sensor is interesting. This is not a normal feature on two stroke EFIs because of relatively low manifold pressures. This inclusion would however give a better picture of the engine load, and add a further degree of accuracy to the fuel calibration.

A knock sensor is also in the system and richens up the fuel mixture to prevent burn downs. This software has a "smart" function that can sense change in resistance if one of the injectors should fail. If this should happen, the other injector is automatically enriched to prevent engine failure. Ski-Doo claims a 50% reduction in emissions and a 25% reduction in fuel usage. The SDI engine also requires less oil, because there is no fuel in the crankcase to wash it through. As a result, Ski-Doo installed a smaller oil pump from their 600 model. Savings in oil consumption is estimated to be 30%, and the smoke emission is drastically reduced.