Re: Evinrude 9.9 HP
This is all theoretical. You did not state the year of the motors so I am going to assume that they are both newer motors who's Hp's are both being measured at the prop.
In theory since the Hp of both motors are the same the work they would do would be the same and therefore on the same boat, their speeds would be the same. The only decernable difference would be their weight, making the two stroke go a little faster than the four stroke. I am sure, however, that this difference could be made up simply by how each is trimmed on the boat and probably quite a few other things.
The question, however could be asked two different ways. The way you asked it was which one would be faster, and the answer should be, that they are both about the same. If the question was asked, which motor would win a race of 5 miles, the two stroke would kill the four stroke every time. This is because the two stroke puts out more torque, since its cylinders fire on every down stroke, where as the four stroke only fires on every 2nd downstroke. What this means is that in a race the two stroke would lung out of the water and pull away from the four stroke within seconds of the start of the race and then with both at WOT, both motors should reach equal speeds. Since the 2 stroke is so far ahead, however, it would win the race, every time. The four stroke would never catch it.
That is my opinion.
