Honda has developed a 110kW (150hp) class outboard motor as the flagship model of its large, 4-stroke engine (4st) outboard series. A variety of technologies have been employed to increase power and reduce weight to produce a 4st engine in a horsepowerclass normally associated with 2-stroke engines (2st) and equal the performance of competitors’ 2st engines.To increase the power of the engine, automotive engine technologies including DOHC-VTEC were employed, together with a dual control cooling system (unique to outboard motors) and a variable intake port system employing butterfly valves.Improved performance was achieved through the application of weight saving technologies including a resin engine undercover manufactured using a new production process and a new oil case structure and the employment of a gear case that lowers the gear ratio to cope with the demands of the large propeller.Increased fuel efficiency has been achieved through the employment of lean-burn using linear air/fuel ratio (LAF) sensor control in a world first for an outboard motor.As a result of the technologies outlined above, a 15% increase in specific power (kW/L) has been achieved in the new outboard against previous Honda models. The motor satisfies the emission requirements stipulated in the 2008 CARB regulations while increasing fuel efficiency by 20% against the previous model in the same output range, and offers an excellent balance between running performance and fuel economy. In actual offshore use the top speed and acceleration of the new outboard match those of competitors’ 2st engines.
Article of Honda R&D Technical Review Vol.16 No.1 (29 - 38)