Can you convert a 20HP Johnny to 35HP with a carb and intake manifold?

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Chris1956

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There was a Utube video where the author claimed he could do the subject. the motor looked to be mid 70's, 2 cylinder. The intake hole in the intake manifold for the 20HP engine was quite small compared to the intake hole in the 35HP manifold.

Is that even possible?

convert 20HP outboard to 35HP - Search Videos

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rolmops

rolmops

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If my memory serves me well, the 20 horse and the 35 horse are different sized blocks. The 35 block is similar to the 28,30.33,40,50,55 block at least as far as size goes.
It is however possible to soup up a 20 horse to produce 35 horse power with some tricks. I would not want to stand close to that outboard , nor have it on my boat. My natural fear of flying metal would stop me from trying
 
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racerone

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Canadian 20 HP model ??----Without a model # you can not expect a proper / correct answer
 
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Chris1956

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The Utube guy says the 20HP motor is about a 1988 model. I just thought the displacement of the 20HP engine was too little for the HP to be raised that much.
 
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racerone

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Agreed.----That 31.8 Cubic inch block was even used for the zephyr sail drive rated at 15 HP.---The earlier models were 35 HP and later the same unit was 30 HP at the propshaft.----So all these ( 20 / 25 / 30 / 35 HP ) models use the same block.----The 15 HP block ( have a new one ) has tiny intake ports.
 
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Mc Tool

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Maybe you could have a look at the crazy Australians and their Dinghy derby race motors....and the racing itself .......pretty berzerk 😁
 
jimmbo

jimmbo

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Same Displacement does not mean it is the Same Block. Porting may be Different
 
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