Late model 15hp faster?

[ChrisAG]

This question can be for all 2-stroke makes, but in particular with regard to the Johnson/Evinrude models from the 1974 and up, there have been many variables over the years, including:

- switch from crankshaft rated hp to prop shaft 198?
- OMC "tuned exhaust" & other changes in 1981 (resulting in increased rpm)
- increase in displacement: 216cc pre-1993, 255cc for 1993+

And finally, competition from newer entries such as 2-stroke Yamahas.

As with others on this board I think the early 15's were a little weak (though stronger than any 9.9), but was that corrected in 1981, and did they get another power boost in 1993?

Does anyone have experience in the old versus new, or Yamaha versus OMC?

 

[JB]

Re: Late model 15hp faster?

Perfect propping and rigging would make more difference than all the above combined.

 

[steelespike]

Re: Late model 15hp faster?

I my opinion a 15 is a 15 with the only difference being the rating change C:
85.No doubt the larger displacement will have a different power curve.
More than likely the exhaust tuning results more in a cleaner burn perhaps better gph (gallons per hour)and smoother trolling.

 

[ChrisAG]

Re: Late model 15hp faster?

Perfect propping and rigging would make more difference than all the above combined.

I noticed that the cavitation plate sits 1.5 inches below the keel. The transom is the normal 15" - the motor seems to be designed to sit too low. Maybe if I let the motor sit on a 1" square piece of wood above the transom there would be less drag.

 

[ChrisAG]

Re: Late model 15hp faster?

I my opinion a 15 is a 15 with the only difference being the rating change C:
85.No doubt the larger displacement will have a different power curve.
More than likely the exhaust tuning results more in a cleaner burn perhaps better gph (gallons per hour)and smoother trolling.

They claimed a higher top speed to go along with the exhaust tuning.

A hp rating seems to be a fair guide but not an exact measurement. I think the manufacturers can be +/- 10% from the stated rating by law. Thus one manufacturer can have a "stronger" engine than the others. On my lake the old 9.8 Mercury had a speedy reputation when compared to the Chrysler 10, for example.