Yamaha/F100TXRX

Because four-stroke technology is relatively new to the mainstream outboard market, some folks are leery about buying them. A big fear is that four-strokes are heavier and make less power than comparable two-strokes. Yamaha took this into consideration when creating its new F100TXRX.
With its weight-saving block, cylinder head and valve-train design, Yamaha engineers created the engine specifically for marine applications. The F100TXRX tips the scales at 369 pounds, which is 63 pounds lighter than Yamaha's own 150- and 200-horse OX66 two-stroke models.
To further reduce weight, Yamaha engineers used lighter materials where possible. For example, the tuned intake manifold is made of a composite plastic rather than cast aluminum, which saves about 5 pounds. But this new four-stroke doesn't compromise performance for decreased weight.
Yamaha's Dan Ostrosky conducted performance tests on Minnesota's Fox River in October. Bolted to the transom of a 3,100-pound boat, the F100TXRX propelled the craft to speeds of 45 mph - not bad considering the power-to-weight ratio.
"This engine can be used on bay boats and on down to walleye boats. It runs very well," Ostrosky says. "We're targeting the large aluminum-boat market."
As an added convenience, the 100 comes with an automatic-choke feature for quick starts in all weather conditions. Once running, a thermostat controls water temperature for consistent performance. Sensors monitor and protect the engine from low oil levels, overheating and blocked coolant passages. If debris or another foreign object blocks a water intake, sensors trigger an alarm to alert the operator and automatically reduce engine speed to 2,000 rpm. This lets a boater cruise to shore without harming the engine