Mercury/Mariner 30/40hp upgrade?

[sutor623]

Hey fellas,

Odd little one carbed motor I just picked up on a new to me boat. Serial is OG211518. Tracks back to a 1996-ish 30hp engine.
Didn't know if anyone had any experience with these motors.

This is a solid block at around 40 cu. in. I was wondering what all needs to be done to up her to a 40hp? Is it the whole carb or just the high speed jet? I also heard that the reed plates are different. Anyone have experience with this?

 

[jimmbo]

Many times engines of different HP share the same Displacement. That does not mean much. Carburation is usually different, as can the reeds. intake manifold can be different, porting in the block, pistons, exhaust tuning and other small differences. Changing the carb jet only changes the mixture, usually resulting in less than original power or a blown engine

 

[sutor623]

I guess at the least it will still have the same lower end grunt.

 

[jimmbo]

I guess at the least it will still have the same lower end grunt.

Not necessarily, to make more power at the top end, low rpm power/smoothness/throttle response is, more often than not, sacrificed.

 

[sutor623]

Well in that case, the 30 would have MORE lower end grunt.

I remember converting an older evinrude 9.9 to a 15hp. She really SUNG top end and added some serious MPH to that jon boat. But, idling was a little rougher and it took a little longer to get on plane.

Guess I will give this little motor a go and see how she does.