Improving performance of johnson 55hp

Chevyls6

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What can i do to gain a few mph and maybe better fuel economy? The obvious answer ive been considering is re-power with a larger engine but my local market hasn't given me any leads.

Im considering doing a re-ring, hone, all new gaskets and shave the head some. compression was kinda low at 105-110 psi last i checked it.
 

F_R

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Ain't going to happen. Even if you were to succeed in getting a couple miles per hour, you wouldn't be able to tell without a GPS or radar gun.

EDIT: Well actually you could play around with props and engine height, etc. But you were suggesting major engine work.
 

racerone

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Compression would be about 150 PSI on my gauge.----Yes it reads correctly.
 

jimmbo

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What Rpms are you getting at WOT? Is the boat rid of unnecessary weight(wife, kids, mother-inlaw)? Is the engine trim and height correct for the speeds it should attain? Is the hull straight and free of Hooks?
As for hopping that engine up? For 1980, OMC did get an addition 5 hp(would about 1 mph faster) out of that displacement, what they did to do so, I don't know, but it was more than just a carb rejet.
 

Chevyls6

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Compression would be about 150 PSI on my gauge.----Yes it reads correctly.

This is what leads me to believe it would benefit from a hone and fresh rings. I have no idea how bad they are after over 40 years of use. I wouldn't be looking to bore it just freshen it up a bit.
 

Chevyls6

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Ain't going to happen. Even if you were to succeed in getting a couple miles per hour, you wouldn't be able to tell without a GPS or radar gun.

EDIT: Well actually you could play around with props and engine height, etc. But you were suggesting major engine work.

Prop is another consideration that crossed my mind. I do not know the wot rpm because there isnt a tach currently.
 

Chevyls6

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What Rpms are you getting at WOT? Is the boat rid of unnecessary weight(wife, kids, mother-inlaw)? Is the engine trim and height correct for the speeds it should attain? Is the hull straight and free of Hooks?
As for hopping that engine up? For 1980, OMC did get an addition 5 hp(would about 1 mph faster) out of that displacement, what they did to do so, I don't know, but it was more than just a carb rejet.

RPM at WOT is unknown because there isn't a tach. Can i use a normal automotive tach hooked to the tach lead off the power pack? I know it would be 2 sparks per rotation instead of every 2 rotations being that its a 2 stroke. excess weight was mostly removed apart from fishing gear, anchor, water supply, fuel, and 2 large men. I do not know what you mean by hooks. the hull is a little curved at the bottom from sitting on the trailer.
 

racerone

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New rings in worn grooves is not the answer either.----As I recall the 76 / 77 / 78 model 55 already had finger ports and was right up there in performance.----Or was it the 79 model that had the finger ports.
 

Chevyls6

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What about the early v4 omc engines? there is a 1965 60hp available for cheap near me and a couple other 1960s examples.
 

Chevyls6

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New rings in worn grooves is not the answer either.----As I recall the 76 / 77 / 78 model 55 already had finger ports and was right up there in performance.----Where is your local market ?

local market is western pa, eastern ohio, northern West Virginia
 

racerone

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That V-4 model 65 is a smooth runner.----But very thirsty.-------A 3 cylinder 70 is your best bet.-----1980 to 1985 models.
 

Chevyls6

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thirstiness is not ideal but smooth running would be a big upgrade. this big 2 cylinder shakes and rattles all the time no unless its at wot
 

Chevyls6

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Anyone know about a 1989 60hp Mariner outboard ? Found one with controls for $250.
 

jimmbo

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Stay away from the pre 69 V4s. while they are simple and easy to tune, they do burn a lot of gas. Their Achilles Heel is their puny Gearcase and very limited prop selection, which is getting scarcer by the day. Plus a lot heavier than the little 2 cylinder 55.
Racers advice about the later version of 3 cylinder 70 is solid.
About the 60 merc. That is likely the old 49.7 in engine, 3 cylinders with 2 carbs. In my Opinion, not one of Merc's better Ideas.

For your info, the WOT range of your 55 is 5000 - 6000 rpm
 

Chevyls6

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Thanks Jimmbo those are important bits of info. I guess that's why the early v4s are so cheap. I found a whole boat with trailer and a 1976 70hp Johnson 3 banger for $450 but I don't know what to do with the boat and trailer haha.
 

jimmbo

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The early years of the 70 did have some teething problems, Like Racer said, a slightly newer one would be preferable. But if you insist on the 76, be sure to inspect the engine(compression, gear oil, etc) Prior to purchase, it is a 44 yr old engine, and again some parts are getting difficult to find. 76 still had the Hydro-Mechanical Gearshift. First thing before you take it out on the water would be a new Water Pump Impeller.
 

racerone

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Sorry ---the switch from hydro-mechanical was made midway through the 75 model year.-----All 1976 models are mechanical shift !-----Lots of newer gearcases bolt right on and will shift the correct way.
 

Chevyls6

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Yeah I surely want to stay away from the electric shift stuff. Why they wanted to make it so complicated is beyond me. Maybe because push button transmission cars were popular back then?
 
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