1956 30 hp johnson

[68chargerfreak]

hey guys i was wondering if there was anyway to make 40 + hp out of a 56 30hp johnson. also was the 56 offerd as a short shaft

 

[JB]

Re: 1956 30 hp johnson

There are numerous ways to re-engineer the RD-18 series engines, but they are all expensive and all distort the torque curve resulting in poor low and medium speed performance.

In that block OMC chose to bore it out to get 35HP in the RD-19, and increase both bore and stroke to get 40HP from the RD-22. They apparently didn't think that messing with carbs, reeds, port timing or compression were a good idea.

So the answer is that yes, it could be done but no, you don't want to even think about it.

 

[steelespike]

Re: 1956 30 hp johnson

Not a quicky change The 30 is 35 cubes the 40 is almost 43 cubes.
If you compare parts lists you may be able to determine other changes.
Stroke is the same on 30,35 and 40 bore is 2 7/8,3 1/16,3 3/16.
Probably short shaft was standard.They were very easy to change to long shaft with a simple kit.Were very easy to get but getting difficult now.Probably used parts would be the way to go.

 

[F_R]

Re: 1956 30 hp johnson

Take the (complete) powerhead off a 40hp Gale and slap it on your 30. Then figure out how to make the hood fit and you got it.

OR

Figure out how to put your hood on a Gale 40 and you got it.

In other words, forget it.