Outboard motor including folded tuned exhaust gas passage

摘要

The invention includes an outboard motor comprising a power head having an exhaust gas port, a drive shaft housing extending downwardly from the power head and including an exhaust gas discharge outlet adjacent its lower end, and a continuous folded passage housed in the drive shaft housing. The folded passage includes a first passage portion having an upper end communicating with the exhaust gas port a second portion extending upwardly from the lower end of the first portion and having an upper end, and a third portion communicating with the upper end of the second portion. The folded passage functions to return to the exhaust port as positive pressure pulses the pressure pulses emitted by the exhaust ports, the folded passage causing return of the pressure pulses in timed relation with respect to closing of the exhaust port to thereby facilitate precompression of the fuel mixture entering the cylinder.