In Examining Today’s Two Stroke Engines, we discussed – and dispelled the misconceptions about – the modern two-stroke outboard motor and explained how it is vastly different from the motors of yesteryear. In this article we will review the attributes of the modern four-stroke outboard motor and see how far they have come in just a few years, dispelling some of their own myths.
Technology and ever-improving engineering have allowed for incredible advances in four-stroke motors in recent years. Common deemed issues with these motors are being resolved with a combination of both new technology and borrowed technology from the automotive industry. Issues of greater weight, sluggish throttle response, and greater complexity along with high maintenance costs are all being addressed and are making the selection of a new motor a more difficult choice due to a greater leveling of the playing field. As had been mentioned in previous articles in this series, there are a few perceived advantages of the modern four-stroke motor. They are said to be fuel efficient, reliable, quieter, smoother, and more environmentally friendly. Perceived advantages of four-strokes are being ever improved and disadvantages are being dispelled.
Certain manufacturers are slowly addressing the issue of four-strokes weighing more than their comparable two-stroke brethren. For example, Yamaha has found a way to increase their displacement without increasing weight. They do this by applying a plasma fusion hardened layer to their blocks that is stronger, 60% harder, and more wear-resistant than traditional steel. By applying this technology, they have not only been able to increase displacement without increasing weight but they are also able to produce lower friction and improved efficiency.
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Other weight-saving features are employed throughout many manufacturers’ four-strokes, such as the choice of new lighter alloy components, the reduction of the number of internal parts and the use of lighter composite cowlings. All of these new features result in the motors being on average only about 10% heavier than comparable two-strokes. In fact, some new model four-strokes weigh less than the older two-stroke motors they replaced, such as with Yamaha’s new 150 hp version. Lightweight alloy blocks borrowed from the auto industry, such as Honda’s 90 hp motor taken from the Fit, the 115 hp outboard from the Accord, and the 225 hp from the Odyssey, are proving to be weight savers.
When a current automotive engine plant doesn’t quite fit the bill, technology from existing motors is applied to an all-new block such as Honda’s 3.6-liter engine found in its new 250 hp motor. Seven Marine even offers a 557 hp outboard that borrows its power plant from GM’s supercharged alloy LSA V8 motor found in the Cadillac CTS-V. Due to its unique high HP rating and relative light weight, this motor is being offered as a weight saver in multiple engine applications. Instead of the need for triple or quad outboards, similar horsepower can be achieved with dual or triple 557’s, thus saving on overall total weight.
Sluggish throttle control and poor low-end torque resulting in unsatisfactory hole-shots has also been an issue that new technology is addressing. Most manufacturers are now providing electronic throttle and shift controls for their mid- and high-range motors. These ‘fly-by-wire’ controls offer sensitive and immediate control and response, all while improving reliability. Other efforts to improve responsiveness include variable valve timing found in the upper end of the Suzuki line, and electronic valve lifting control found in Honda’s motors equipped with VTEC technology. This technology, borrowed from the Acura NSX supercar, provides better economy as well as a broad, flat torque curve and smooth power delivery from idle to full throttle.
While higher maintenance costs for four-strokes is a factor by nature of their design, some manufacturers are doing what they can to minimize cost of ownership. Some manufacturers’ models now do not require periodic valve adjustment service at the rate previously required. Simple service requirements are being made easier to accomplish by the owner such as oil changes, anode replacement, fuel filters, gear oil replacement and even impeller and water pump housing replacement. Now do-it-yourselfers can do most of the basic maintenance themselves. Of course there are service items that should not be attempted by anyone other than a certified technician and it is important to see what maintenance service is required, as this can end up being a significant cost post-purchase and can significantly increase long-term cost of ownership.
One major deciding factor in selecting a new four-stroke motor is its fuel economy. By nature of its design, it can be a reasonably fuel-efficient motor at most RPMs. However, new technology is further improving fuel consumption. Most major manufacturers are providing ever more efficient fuel injection and have tweaked the injection to provide optimum performance and economy. Manufacturers such as Nissan/Tohatsu are touting improved direct fuel injection (similar technology to that of which we wrote about in the last article used on modern two-strokes). Their cylinder heads and piston domes have been redesigned to achieve ideal combustion of the fuel at all power ranges. Add to this ever more finely atomized fuel mist and the result is much improved fuel economy.
Honda’s recent contribution for increased fuel efficiency is its LEANburn Control™. Their motors automatically sense and seek the optimum fuel-to-air mixture at all throttle ranges, resulting in a claimed 10-25% increase in fuel economy. Suzuki also touts its lean burn fuel-to-air mixture control with similar results. Suzuki is even offering battery-less fuel injection and lean burn technology in motors as small as 15 and 20 hp. Even cowlings are being modified to improve efficiency; Honda’s new dual vent cowlings boast improved cooling and efficiency and look pretty snazzy to boot. Improved design in the lower unit’s gear housing not only is allowing for more robust gearing but is also seeing improvements in hydrodynamics, resulting in further efficiency, such as those found in new Suzuki, Mercury and Honda motors. All these advancements in technology have increased already-improved efficiency.
Reliability is another perceived value of four-stroke motors. Yamaha showcased motors recently at the Miami Boat Show that proved the extreme end of reliability in an outboard. They had 150 hp outboards (their best selling motor) that were still running strong after over 6800 hours of commercial use. Averaging 300 miles a day as power for a commercial water taxi, they still tested out strong in compression tests and are still fully functional. If maintenance schedules are followed there is no reason not to expect long-term reliability out of any of the manufacturers producing outboards for the US market today. In fact, some manufacturers are touting reliability as one of the main features of their four-stroke offerings.
As technology progresses so does the allure of the four-stroke outboard. As most major manufacturers are focusing on four-stroke power plants and competition is fierce, the end result is a marketplace with a wide range of very good motors that are ever more efficient, reliable and provide power and responsiveness at all power ranges. There has never been a better time to be in the market for a four-stroke outboard.