115 performance mods

[Kevin O'Connell]

Has anyone done performance mods to increase power on Johnson 115hp outboards? I'm interested in things like milling heads for increased compression, performance reeds, airbox mods, carb mods, etc.
Anyone got info?
Also, what symptoms would reveal bad reeds?
I also, have low idle RPM even after adjusting idle speed and it causes stalling- any ideas?

 

[ezeke]

Re: 115 performance mods

No one can give you reliable information without knowing the year/model of your engine.

 

[tashasdaddy]

Re: 115 performance mods

unless you are a very experienced mech, it is a good way to ruin and perfectly good motor.

 

[Silvertip]

Re: 115 performance mods

The best way to determine IF you can get increased power out of your engine is to compare the specs on your engine to the next higher HP version of your engine. If you see bore and stroke differences, there is a pretty good chance your engine block is already at the top of its HP range. If the manufacturer was able to get more power out of it (reliably) they would have done it. If your engine is the same block as the next higher HP version, you need to compare the entire engine parts lists and see which parts differ. Those are the parts you need to change. Eliminate one of them, like block porting, and you will have spend lots of money for very little gain. You will also find the cost of those parts extremely prohibitive for what you want to achieve. If you need more power, sell yours and buy what you need.

 

[iwombat]

Re: 115 performance mods

You also want to be really clear as to what you want to get out of it. Hole shot and top speed are different and sometimes mutually exclusive performance mods. It's also not going to be cheap and could even exceed the price of selling yours and buying bigger.

 

[xxturbowesxx]

Re: 115 performance mods

to put it into perspective you may be able to inch maybe 10-20hp out of that motor by throwing alot of money and time into it. At that point you might as well just sell the motor and buy a more powerful one(if its under your max hp). your talking about porting,shaving heads,new reeds,exhaust tuner..

 

[Faztbullet]

Re: 115 performance mods

There are some bolt on mod's and tricks that can add some performance to your engine but major HP gains will will cost ya like everyone has posted. Do you have a crossflow or looper engine?

 

[cdoliver]

Re: 115 performance mods

does it spit fuel out the front of the carbs when running? (that would be a sign of bad reeds) You might just have clogged idle jets. Clean the carbs.

 

[Kevin O'Connell]

Re: 115 performance mods

Its a 1975 115 hp V-4. I'll try cleaning the idle jets and the rest of the carbs.
If I could get an extra 20 hp out of it without huge expense, I'd do it, but beyond about $500 I won't. So what's available for that much?

 

[iwombat]

Re: 115 performance mods

Again, what are you aiming to get for those mods, more speed or more pulling power?

 

[crb478]

Re: 115 performance mods

unless you can find a simular vintage 135 hp to steal parts from for cheap you are not going to get 20 hp for $500.00. I believe that even with the 135 you would still have to do a little machine work to make it fit. Best bet would be to maximize the set up you have now raising the motor as high as possible without cavation. Either that or sell the motor and take the extra 500.00 and look for a newer looper motor.

 

[Dhadley]

Re: 115 performance mods

There are some "tricks" you can do to that powerhead very easily. However, in performance world, the gearcase shape is going to be a big downer.

What hull do you have? What are you looking for?

 

[Kevin O'Connell]

Re: 115 performance mods

I've got a '66 Larson Lapliner. It runs about 45mph now and I'd like to see more speed out of it.
What parts need to come off a 135- exhaust baffle and carbs?
What about a 140?
What tricks are you referring to?
I'e got the motor on a jack plate as high as possible already.
Would a nosecone with a low water pick up help? If so would raising the motor higher help?
What about trim tabs?
Should the fuel tank be in the rear or front for the most speed?

 

[Dhadley]

Re: 115 performance mods

The problem is that hull does not respond well to small increases in torque and / or prop rpm. What is your top rpm now?

At 45 mph a nosecone will most likely hurt performance.