83' Johnson 90 mod to 115 specs?

[zaneh]

I have a 78' 115 V4 Johnson with a bad cylinder (broken ring), and have a chance to get an 83' 90 V4 Johnson. Is it possible to use the carbs and exhaust plate from the 115 on the 90 to get more performance? Also were there any porting differences between these? I'm new to these Johnsons and any help would be greatly appreciated! Thanks in advance.<br /><br />Zane

 

[bp21]

Re: 83' Johnson 90 mod to 115 specs?

Hi there zaneh,<br /><br />Word here on the board is that generally speaking, if you want to upgrade an engine to get more performance, you would be better off just purchasing a bigger engine...much cheaper in the long run without the headaches of a revamped motor.

 

[Dhadley]

Re: 83' Johnson 90 mod to 115 specs?

Yes all the parts you have will interchange. The exhaust plates are the same if they are both flat. The carbs should be close to the same. If you use a larger venturi you will have less on acceleration but slightly more on top end. If you use a smaller venturi carb you will have more acceleration and slightly less top end. But since you coked a piston and broke a ring your motor most likely doesnt turn enough RPM now. Look at your set up to gain speed and reliability no matter which motor you use.<br /><br />Good luck!

 

[zaneh]

Re: 83' Johnson 90 mod to 115 specs?

Dhadley,<br /><br />Thanks for the input. I guess I should have been clearer in my 1st post. I bought this engine and boat and knew it had 1 bad cylinder when I bought it I have never actually run this combo. The prior owners setup looks fine as far as prop etc. It probabally was a lean condition I'll address later if I use the 115 carb setup. Now back to my original question. Is there a difference in carbs from the 90 to the 115 or did they just run different jets? Also does anyone know if the porting is different between these two engines? I have alot of experience building performance marine engines, mainly mercs, but really don't want to tear into a good running 90 and have to rering etc, just to modify the ports. Thanks again.<br /><br />Zane

 

[Dhadley]

Re: 83' Johnson 90 mod to 115 specs?

look at the front of the carbs. The venturi size is cast into the carb body. That will tell you if they are the same or not. Carbs are jetted for the venturi size not the horsepower. That is why we can run a set of 1 inch carbs off of a 150 V6 on a V4 and vise versa. When we used to race the crossflows we would use small venturi carbs for acceleration and larger ones for more top end.<br /><br />The big difference on the porting is going to be the intake ports. The exhaust will most likely be close. If the intakes (and/or exhaust) are smaller on the 90 you can open them up very easily if the motor is apart. Just measure the 115's and open up the 90 to match. They are centered the same. <br /><br />You can also put on a "bubbled" exhaust and help some. Once you run the motor and see where you are then you can go from there. If the motor only turns 5500 rpm the porting may not help a lot anyway.<br /><br />Good luck!

 

[zaneh]

Re: 83' Johnson 90 mod to 115 specs?

Dhadley,<br /><br />Thanks for the info. If I go with the Johnson 90 horse, it will be on a 78 Glastron/Carlson CVX-16 so I would like all the performance I can get out of it. The prior owner said the 78' 115 Johnson ran an indicated 47 mph with a 19 pitch aluminum prop @ 5400 rpm. I think he was stretching it but you never know. Thanks again.<br /><br />Zane

 

[Dhadley]

Re: 83' Johnson 90 mod to 115 specs?

Very cool boat! At only 5400 RPM I wouldn't expect the motor to live long. You need to get the R's up. Start with raising the motor (watch the water pressure) and a good stainless prop. I think 19 is in the ball park although his speedo may have been very kind to him. <br /><br />With a good 19 and RPM's at 5800 to 6000 you will definately be in that range or slightly faster. You may want to think about a jackplate also especially if you go to a 4 blade stainless.<br /><br />Good luck!