How to make 90hp outboard into a 115hp

[Qcarver90]

I have a 2003 90hp oil injected 2 stroke outboard. I know that on the same year Mercury made this outboard in a 115hp version. What would I have to do to give the engine the extra 25hp. The only thing I can think of is larger carbs or more timing.

 

[Qcarver90]

Also if someone could give me the Serial numbers of a newer 90 and a 115hp outboard I might be able to look on mercurypartsexpress.com and find out what parts are different

 

[Chaney101]

Re: How to make 90hp outboard into a 115hp

keep me posted because I would like to know the outcome

 

[Boatin Bob]

Re: How to make 90hp outboard into a 115hp

No way for you to do this. The 115hp is a 4 cyl with 4 carbs. It's also a 2 + 2 motor meaning it only runs on 2 cyl up to approx 1800 and then the 2nd 2 cut in.

 

[Texasmark]

Re: How to make 90hp outboard into a 115hp

Other thing is the 90 is a 2.3 gearbox and the 115 around 2.0. I'm running the highest pitched medium gearcase prop on my 90 (24XP) I can buy (commercially) on it now. If it were a 115 I couldn't prop it....course if you have it on a tub (no offense intended) then that part is not a problem as you are probably already down in the lower pitches and you have room to grow.

 

[Qcarver90]

Re: How to make 90hp outboard into a 115hp

No way for you to do this. The 115hp is a 4 cyl with 4 carbs. It's also a 2 + 2 motor meaning it only runs on 2 cyl up to approx 1800 and then the 2nd 2 cut in.

No the engines for my 2003 model year use the same 3 cyl block for the 90 and 115 also for everyone else the engine is a 90ELPTO Serial:OT698029

And I have a 115hp lower unit on my motor because the original 90 lower gears disinagrated and I could only afford a used 115 lower unit to put in its place

 

[Texasmark]

Re: How to make 90hp outboard into a 115hp

Okayeeeeeeeeeeeeee.

Looks like you have most of the bases covered.

I have a Merc manual that covers my engine that is probably superseded by another manual for yours.....mine jumps from 90 to 125 4 cyl.

In the manual jets are listed for different engines and obviously they are different depending upon engine hp.

You might go to your local Merc dealer and get a set of carb jets for the 115 and start with that. While you're there, you might ask the mechanic or see if they will let you look in the parts list and see what parts are different between engines.

25 hp increase is pretty stout to get with just jets (sometimes rated rpm's are higher too), but what do I know....my 90 hp is rated at 5500 rpm max; maybe the 115 is rated at 6000 (which some engines are).

HTH

Mark

 

[Boatin Bob]

Re: How to make 90hp outboard into a 115hp

No the engines for my 2003 model year use the same 3 cyl block for the 90 and 115 also for everyone else the engine is a 90ELPTO Serial:OT698029

OK....whatever you say...I'm not going to argue but I have a 2003 115 Merc 2 stroke and I know it's a 4 cylinder 2 + 2...good luck!

 

[Silvertip]

Re: How to make 90hp outboard into a 115hp

Carver -- heed the advice! The 75 & 90 are three cylinder blocks. The 115 is a four cylinder. Unless you own a machine shop and are good with a welder, you aren't going to make 115 out of a 90. Directly from the Mercury brochure: 115 Classic = 115 HP, 4 in-line, 113 CI (1848 cc) 3.5" Bore, 2.93 Stroke.

90 Classic = 90 HP, 3 in-line, 84.6 CI (1386 cc) 3.5" Bore. 2.93" Stroke.

So you see, you need to tack on one more cylinder to your 90 to make it 1848 cc.

 

[jimmbo]

Re: How to make 90hp outboard into a 115hp

Merc does make a 3 cylinder 115

http://northamerica.mercurymarine.com/engines/outboards/optimax/onefiveliter_specs.php?ID=52

 

[Qcarver90]

Re: How to make 90hp outboard into a 115hp

Merc does make a 3 cylinder 115

http://northamerica.mercurymarine.com/engines/outboards/optimax/onefiveliter_specs.php?ID=52

Thats what I have been saying. And if you look at the 90hp version of that motor on the sight it still has the same bore, stroke and everything except gears. But I need to what gives it the extra 25hp.

 

[WillyBWright]

Re: How to make 90hp outboard into a 115hp

The three cylinder OptiMax motors referred to in that webpage come in 75, 90, and 115Hp. The computers are different and the air intakes are different. There might be more, but the price of the computer alone makes the upgrade economically unfeasible

Right now what you need to do is figure out exactly what you have, because it ain't no OptiMax. The first commercially available ones were 115Hp and that wasn't until 2004. The 75 and 90 versions came out later. If you have a 2003 90 triple, it has to be a carbureted oil injected 2-stroke. There was never ever ever a 3-cylinder carbureted oil injected 115. 90 is as big as conventional triples got.

If yours is an Opti, it'll say so on the hood. If it doesn't have OptiMax on the hood, it ain't (unless somebody stuck some stickers there to fool you).

Addendum: I just plugged your serial number into the Mercury Parts Express website and one of the pages showed Carburetors. Your's ain't no Opti, and you can't make it a 115 without squeezing another cylinder into it. I hope that puts this debate to rest. Sorry.

 

[Silvertip]

Re: How to make 90hp outboard into a 115hp

Willy -- Are you anticipating one more question! Such as: What's the difference between --------------? or Why do Opti's have ECMs and carbed don't?

 

[Texasmark]

Re: How to make 90hp outboard into a 115hp

Well at least the gearbox is 2:1 on the Optimax 115 and like I said, if he could tack on that extra cylinder, he'd have to have a special prop built cause of the 2.3 gearbox.

Personal opinion here. I don't know how far you can stretch a 2 cycle cylinder diameter and get reliable operation. I did however, notice that the Optimax was sporting the same cu in displacement as the smaller engines indicating that they used something besides brute force to achieve their higher hp. Hope it works out for them.

Mark