The performance gap narrowed quickly, however, as builders learned how to fine-tune four-stroke induction systems to create more power and computers took over the injection process to create optimum power across the power band. Consider today's big four-strokes as virtually indistinguishable from two-strokes in performance, making your buying decision more complicated.
In the midst of all of this, Mercury introduced its Verado series, a radical departure from the norm in the form of a supercharged four-stroke engine. "Verado is a four-stroke, small-displacement, fuel-efficient design that creates both torque and power output through supercharging," says Claus Bruestle, Mercury's vice president of research and development. "We are creating up to 275 horsepower out of a 2.6-liter inline-six block. Of course, running a supercharger also costs you some horsepower as well, but overall it's the most efficient way to do it."
Other companies have taken a different approach to the same problem. Suzuki, for instance, just introduced a 300-hp four-stroke at the Miami Boat Show, the most powerful four-stroke model yet built [see review] - although both Yamaha and Mercury now offer 300-hp two-stroke models. The new Suzuki takes the opposite approach from Verado in creating horsepower and torque.
"Our new 300 is a large-displacement, naturally aspirated engine that uses our proven 55-degree block and offset drive shaft," says David Greenwood, senior product planning engineer for Suzuki. "This design allows us to build a remarkably small, yet powerful engine that will be similar in size to other people's 250s." Suzuki has not yet disclosed the engine's weight, but Greenwood points out that, like all Suzukis, the 300 will run on 87-octane fuel. The top-of-the-line 275-hp Verado requires 92-octane.
Suzuki, Honda and Yamaha all utilize high-tech variable valve timing, which allows their engines to create optimum power on both ends of the power band and substantially lowers emissions. "Variable valve timing and electronic lift control uses low-profile cam lobes below 4,500 rpm," says Robin Senger, Honda's marketing manager. "Above 4,500 rpm, high-output cam lobes engage to optimize performance at the top of the power spectrum."
Yamaha also uses variable valve timing, along with other state-of-the-art technologies, to keep its outboards clean and efficient. "We see a strong consumer preference toward larger-horsepower four-stroke technology," says David Meeler, Yamaha's technical marketing manager. "We have provided clean, efficient power to meet this demand using innovative engine designs, such as variable valve timing and computer-controlled single air intakes."
Bombardier has taken a decidedly different approach to the technology question, relying solely on direct-injected two-stroke technology in its line of Evinrude E-TEC outboards. The company claims that E-TEC two-strokes run cleaner than competing four-strokes and emit much less CO than comparable four-strokes - up to 86 times less at slow speeds.
Bombardier also points out that E-TEC outboards burn the two-stroke engine oil in the combustion process. The highly stratified fuel/air charge burns so completely, no oil escapes into the environment. The oil in four-strokes must be drained at regular intervals and then disposed of, which makes direct-injection two-strokes inherently cleaner since improper disposal of used motor oil constitutes a major environmental problem.
Tohatsu has also chosen the two-stroke route with its line of TLDI direct-injection outboards, ranging from 40 to 115 hp. "We feel the two-stroke TLDI system is a better way to go in the higher-horsepower engines than four-stroke," says Jennifer Pharris, Tohatsu's assistant advertising and marketing manager. "You get the weight savings plus that 'oomph' that people have come to expect from outboard power."
Other innovations have occurred in the form of electronic engine control and monitoring, too. Mercury's SmartCraft system consolidates all engine monitoring and diagnostics into one easy-to-use LCD panel, and Yamaha's new Command Link does essentially the same thing. Command Link utilizes a Local Area Network (LAN) and a series of hubs to route an incredible amount of information to one of several different digital displays. And you can display information from external sources like depth sounders and GPS receivers. Suzuki also has a fly-by-wire system under development.
Mercury's digital Shadow technology takes things a step further. With the recent trend toward triple- and even quadruple-outboard power, Mercury developed new controls to make driving these engines easier. Shadow technology uses a two-lever control head that makes the middle outboard(s) "slaves" to the outer engines, which means that one lever controls more than one engine. No more fumbling around with six or eight throttle and shift levers while docking. It also automatically synchronizes multiple engines and makes the transfer between helm stations seamless.