Increasing the power of a 1963 Johnson 5.5 hp

[BrianB]

Hello all,
Just got an 8 foot inflatable RIB. It could take a 10HP, but I am using my trusty 1963 Johnson 5.5, which is the same age as I am! Knowing that many motors are rated for different horsepower using different carbs, does anyone know whether I could increase my motor to a higher power like 7.5 or 10HP? And, how to do it? Thanks in advance,
Brian in central NY

[Mumbles]

The easiest power gain would be by bolting on a later six horse powerhead but that would present all kinds of challenges if you wanted to use the original hood. The starters and carbs are completely different. Without buy a larger motor, I think you are stuck with 5 1/2 horses.

Here’s a ’63 CD we’ve had since new and we figure it has less than 100 hours on it.

[billw]

I always wondered why they sold so many 5 1/2s. I know, I know, they are fantastic-running motors; but they are too heavy to be easily portable and yet too low power to give most boats a decent speed….

Long live American manufacturing!

[fleetwin]

Yeah, not much you can do with the 5.5s to increase power… This engine will never make enough power to plane some of those short inflatables…. This is a great fishing motor, but not much power. Sorry….

[crosbyman]

everything has a purpose… JW CD AD s are great fishing motors and keep you from rowing back to camp when the big kicker dies

Joining AOMCI has priviledges 🙂

[jcrigan]

It would seem that getting the maximum rpm at full throttle is what you may be looking for. How about starting with a lower pitch prop. Then carrying the least amount of weight overall. Non ethanol fuel may carry more btu’s per gallon. All in all, you may not notice much if any improvement unless there is another like boat to compare to.

[amuller]

I have one of these–same year–and agree with the opinions here. Nice motor, but heavy to carry around and not much get-up-and-go. My thought would be to get a 7.5. These are easily found–lots and lots were made!–and are very similar mechanically. Next step up in this family of motors would be a ten. These are definitely heavy but have the advantage that the pump can be serviced without lifting the power head.

[fleetwin]

The newer style 6-8hps made in the 80s-90s are a great choice also….More power than the old 5.5-6hps, but still light….

[JOHN HOLBIK]

Early fifites 7.5 evinrude 49 lbs

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