Upgrading a '69 55 horse to 60 or 70 horse

[rolmops]

How should I go about upgrading my 3 cylinder 1969 '55 Johnson to sixty or seventy horse? I am looking for a winter project to keep me from under my better half's feet and whip.

 

[rodbolt]

Re: Upgrading a '69 55 horse to 60 or 70 horse

hello<br /> get a second job and buy a better engine .I have seen many attempts at modifying that engine for 65-70 horses. some worked most burned pistons. witout a dyno or a test wheel it is almost impossible to tell if your going ahead or astern. this motor ,other than the amplifier was a very good one in stock form.<br /> good luck and keep posting.

 

[Chinewalker]

Re: Upgrading a '69 55 horse to 60 or 70 horse

Hi Rolmops,<br /> There's a lot more different between the 55 and 70 than a carb change and some timing. The entire block casting is different, as the ports are cast into the cylinder walls. The exhaust chamber is completely different, too. The later 70s/75s used heavier conrods as the first couple years of the 70hp used the original 55-designed rods and they were letting go. Lots of other differences, too, but the bottom line is to either stick with the 55 configuration, or put your 55 hood on a 70 and go from there...<br />- Scott