In the U.S. market, BRP, the parent company of Evinrude, is alone in remaining devoted to the development of 2-stroke outboard motors. That devotion recently
resulted in the new series of 1.9-liter Evinrude outboards with the latest E-TEC G2 direct injection technology.
The Evinrude 115 H.O., Evinrude 140 and Evinrude 150 share a three-cylinder power head that incorporates a number of design features previously available only on V-6 Evinrude E-TEC G2 outboards, the first of which debuted in 2014. The 1.9-liter models are not quite as feature-laden as the V-6 Evinrudes, but are available with integral power steering, standard digital throttle and shift control, and a 1.9-gallon oil reservoir below the power head. A pair of balance gears cancels the primary vibration of the triple-cylinder engine. The star of the show, however, is the E-TEC G2 system; it’s the second generation of E-TEC direct fuel injection.
Direct injection for 2-stroke outboards first appeared in the late 1990s with the OMC Evinrude/Johnson Ficht DI system, Mercury Marine OptiMax DI and Yamaha HPDI system. Each allowed a 2-stroke engine to meet modern exhaust emissions regulations. Mercury, Yamaha and Suzuki also started developing outboards with 4-stroke engines and electronic fuel injection in the intake tract, a setup that also met emissions regulations but that resulted in an engine significantly heavier than a 2-stroke of the same power.
A 4-stroke engine has moving intake and exhaust valves, which can seal the
combustion chamber until all the fuel is burned and then allow it to escape before an incoming charge of fuel and air enters the chamber. This is the kind of engine found in most automobiles.
A traditional 2-stroke engine is much less complex. It uses the moving piston to open and close intake and exhaust ports as it pumps a mixture of fuel, oil and air from its crankcase to the combustion chamber. In that cycle, however, a significant amount of unburned fuel can escape through the exhaust port, resulting in sky-high hydrocarbon emissions (evidenced by the cloud of smoky exhaust many of us recall from the past). Because it does not require valves, a camshaft and many other parts, the 2-stroke is relatively cheap to manufacture and lightweight.
Direct injection retains the 2-stroke advantages while producing acceptable emissions. It injects a fog of fuel directly into the combustion chamber quickly, timed to prohibit unburned fuel from escaping through the exhaust port. This has to be accomplished in a fraction of a second. The Mercury OptiMax system used compressed air to blast atomized fuel into the engine. Yamaha HPDI used a high-pressure fuel pump. The BRP E-TEC system uses electromagnetic “voice coil” technology to activate a steel ram that pushes the fuel at 800 psi through outwardly opening swirl nozzles into the engine, while atomizing fuel down to 25-micron droplets that are easy to ignite.
Another advantage of direct injection is its ability to operate in stratified mode at low engine speeds, when a small column of fuel vapor is injected into the combustion chamber adjacent to the spark plug, and the rest of the cylinder is filled with air. In this way, the engine gets just enough fuel to continue running at idle or low speed, and emissions and fuel economy are outstanding. When the throttle is advanced, the DI system reverts to filling the entire combustion chamber with a homogeneous fuel/air mixture.
E-TEC G2 is the latest BRP refinement of this technology, developed with computer modeling tools that helped devise new combustion chamber and piston shapes, porting designs and an injector. The result, according to BRP, is a motor that offers outstanding midrange torque and low emissions, with fuel economy that may be 100 percent better than a 4-stroke outboard’s at trolling speed. (Note that a direct-injection 2-stroke still requires a mist of oil to be created in the crankcase to lubricate bearings, so there’s an oil reservoir required either in the boat or on the motor. A 4-stroke has a sump of oil that needs to be changed annually.)
Direct injection works on a 4-stroke engine too, and it is a design feature of the new 425-hp Yamaha XTO outboard. In a 4-stroke, direct injection improves power and efficiency. Yamaha and Mercury have stopped producing direct-injection 2-stroke outboards (Tohatsu still builds a few), but the latest-generation 4-strokes weigh the same as 2-strokes and offer the latest digital advances.
So, the recreational boating market has voted for 4-strokes, but BRP, probably to the delight of Ole Evinrude, continues to wave the 2-stroke banner.
This article originally appeared in the August 2019 issue.