We’ve all seen boats plowing along with their bows up in the air, trying to get on plane. Sightlines forward are lost, and it can become a real safety factor if boaters can’t see where they’re going.
A 2-stroke engine design, such as the Evinrude E-TEC G2 outboards, has a power stroke on every turn of the crankshaft. But 4-stroke engines have only one power stroke out of four strokes and two turns of the crankshaft. That means at any given RPM, more power is produced by the 2-stroke engine – theoretically, twice as much. For example, at 2000 rpm a 2-stroke engine fires 2,000 times, but a 4-stroke engine fires only 1,000 times. With half the combustion, there is no way a 4-stroke engine can produce the power and torque of a 2-stroke, unless its displacement is twice as much, in theory.
The more horsepower that is available at the low RPM range — say from 500 to 3000 — the more power there is applied to the crankshaft, and the greater the torque. Since every turn of the crankshaft on a 2-stroke has the piston completing its power stroke, roughly twice as much power is applied to the prop shaft than with 4-stroke engines with the same horsepower in the low- and mid-RPM ranges.
Greater torque makes it easier to pull water skiers and wake boarders out of the water, and in one case a boat fitted with three 300-hp Evinrude E-TEC engines pulled 54 skiers off a dock from a standing start. It was the tremendous low-end torque that allowed three engines to pull over 8,000 lbs. (3,629 kg) of skiers from a standing start to a standing finish.
In a now famous independent test of a 150-hp E-TEC G2 vs. a 200-hp 4-stroke Yamaha engine on a 25’ (7.62 m) center console, the 200-hp 4-stroke could not get the boat on plane, even though several different props were tried. The fastest the boat would go with the 200-hp Yamaha at full throttle was 10 mph with a low-pitch prop. But when the Evinrude 150 was put in the water, the boat got on plane in 12.1 seconds and reached a top speed of 27 mph. This test was repeated with different props (including props recommended by the engine makers) on both engines, and nothing could be done to get this 4,300-pound (1,950 kg) boat on plane with the 200-hp 4-stroke Yamaha.
Even though both engines were rated at the same horsepower, the 2.8 L inline 4-cylinder Yamaha could not match the torque of the 2.7 L V6 Evinrude E-TEC G2. The added power of the 2-stroke engine plus the additional displacement of the Evinrude simply produces prodigious torque compared to a 4-stroke engine with less overall displacement – even though it is rated at the same horsepower.
This comparison of the torque curve of the Evinrude E-TEC 225-hp outboard compared to a 225-hp 4-stroke engine, shows that in the low-rpm range the Evinrude has 32% more torque. In the mid-range it has 27% more torque, and even at the high end the 2-stroke Evinrude has 16% more torque than the 4-stroke engine.
The data surrounding a 2-stroke engine may seem remarkable, and even surprising, as many boaters bought into the idea of 4-strokes when they were first introduced in the 1980s and never looked back. These were the days when 2-stroke engines were using old technology, were smoky, hard to start, and oil had to be added to the fuel. But, the Evinrude E-TEC G2 2-stroke design changed all of that.
BoatTEST.com does not make these statements lightly: We draw our conclusions based on more than 40 tests we have conducted with Evinrude engines.