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

rolmops

rolmops

Vice Admiral
Joined
Feb 24, 2002
Messages
5,567
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
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,370
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

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,857
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.
 
M

Mc Tool

Chief Petty Officer
Joined
Aug 7, 2024
Messages
595
Maybe you could have a look at the crazy Australians and their Dinghy derby race motors....and the racing itself .......pretty berzerk 😁
 
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