Help on how to mod an 1980 Johnson V4 85hp

[spybot]

Hi guys i h ave a 1980 85hp Johnson V4 i have read that this is the same block as the 115HP i know the heads are almost the same and the main diffreance is in the carbs (the throat size and jetting )
Please help if you can with any ideas on how i can squeeze some more power out of her. I dont want an unreliable race boat but a fast lake boat. that i know i can sput the key in and it will start everytime
Iam looking into porting and internal mods.

 

[interalian]

Not just carbs. 115 has much larger intake ports. You won't get the power bump without the ports.

 

[spybot]

Hi Interallan i dont mind doing the porting work. i have seen some where there was a 9 page guide but that was for a 220 v$ how can i find out the correct port size ?

 

[spybot]

Hi again i just started reading your rebuild This is exactly he info i need. Hope you dont mind if i ask a few questions

 

[flyingscott]

Hi guys i h ave a 1980 85hp Johnson V4 i have read that this is the same block as the 115HP i know the heads are almost the same and the main diffreance is in the carbs (the throat size and jetting )
Please help if you can with any ideas on how i can squeeze some more power out of her. I dont want an unreliable race boat but a fast lake boat. that i know i can sput the key in and it will start everytime
Iam looking into porting and internal mods.

It would be cheaper to buy a 115 hp.

 

[spybot]

Hi Flyingscott thanks for the input. i have read a good few of your posts on other forums. I know it would but if i build it i know it will be like new again. Plus iam in Scotland so not so many 115s to be had at a cheap price

 

[interalian]

Hi again i just started reading your rebuild This is exactly he info i need. Hope you dont mind if i ask a few questions

Ask away. My build took a 140 block, carbs and exhaust bubble, and mated them to my old 90 leg. I used the 90 crank as the 140 had a damaged center bearing from a misaligned dowel on a prior rebuild. Careful research showed no differences otherwise.

 

[Chinewalker]

You'll be much further ahead if you start with a 115 or 140 block. Opening ports up isn't as simple as opening e ports up.

 

[Faztbullet]

Opening up ports just helps it breath...port heights is the difference. The most HP you will get out of a flat back is 90HP at prop..

 

[ondarvr]

And you're starting with the older crank rated HP motor at 85HP, a 90 (rated at the prop) from just a few years newer will have more power.

​Run it as is and saving money for a bigger motor is a good option.

 

[interalian]

Opening up ports just helps it breath...port heights is the difference. The most HP you will get out of a flat back is 90HP at prop..

Exactly. My 140 Frankenmotor (crank rated) is about 115 at the prop. The orignal 90 (also crank rated) was probably 75 at the prop, so any way you look at it I'm up 40+hp over my original. My little tin boat has never gone so fast - I'm over-revving close to 50mph at 3500' with a 17" wheel. Looking at a 19" wheel and passive trim tabs now.

 

[flyingscott]

I agree look save up your money because you may be surprised how much it will cost you to do all that work. The motor I would recommend if you could find one would be the later 110 hp Evinrude/Johnson motors. They have the bubble back exhaust and all the other goodies you will need. They are also prop rated motors.