Two stroke adds gas every revaluation of the motor to every cylinder, 4stroke adds fuel to each cylinder every other revaluation. This is why four strokes need more displacement than 2 strokes to make the same power. Now if you take technology and a more efficient 4 stroke it has potential to make more fuel economy but at the risk of burning it up, so a 200-300 hp outbourd that is not pushed to the ragged edge of power should last longer, they could make a NA 2.0L 4 cylinder to make the power but it wouldn't last thousands of hours at redline like the 4.6 will