25 to 35hp conversion?

[Dieseltech910]

So I was talking to some people the other day and we got on the subject of outboards. I mentioned that I’m running an 82 Johnson 25hp. One of the guys said that it’s the same motor as a 35hp and all I’d have to do is put a 35hp intake and carb on to turn my 25 into a 35. Anybody know if there’s any truth to this?

 

[flyingscott]

Yes it can be done it's a little more involved than the carb and intake there is a timing change also. The problem you have is your lower unit will not handle the power. Your lower unit is borderline for the 25 hp a 35 hp will wreck it. The 1985 and newer motors have a common lower unit. Your motor has the old style lower without through hub exhaust different from the 35.

 

[Dieseltech910]

Yes it can be done it's a little more involved than the carb and intake there is a timing change also. The problem you have is your lower unit will not handle the power. Your lower unit is borderline for the 25 hp a 35 hp will wreck it. The 1985 and newer motors have a common lower unit. Your motor has the old style lower without through hub exhaust different from the 35.

What about going to 30hp? Any issues doing that?

 

[flyingscott]

5 hp is not going to make the difference you think it is. The 28 hp used a similiar lower to what you have. If you want.a bigger motor sell yours and buy one.

 

[jimmbo]

The Two engines have the same displacement. Carbs, Intake, Reeds, Blocks, Exhaust manifolding, are some of the differences in the powerhead, it was pointed out above about the difference with regards to the Lower Units. The Midsections and transom/swivel Brackets are different too.

 

[Tim Frank]

There are numerous threads in here about changing this or that to increase horsepower.
I have not seen one end well so far.

There are also lots of threads in here by people who have purchased an outboard from some tyro who has "re-engineered" the motor and ended up selling it to just buy the bigger motor....and the buyer is left to work out why their purchase does not run very well.

Reverting back to OEM design solves the problem(s)..... in most cases.