need help with my 115 hp Merc - please!

[nbpbborg]

anyone know if and how a 1992 115hp merc can be converted to a 125 hp merc? Same CID, is it carb jetting or port timing, or both?

 

[freddie]

Re: need help with my 115 hp Merc - please!

I believe the block is the same ,but the lower unit gear ratio may be different, the carbs may have alarger bore on 125hp. Check with a merc dealer for exact specs. may be a costly conversion!

 

[nbpbborg]

Re: need help with my 115 hp Merc - please!

I know the lower unit is the same - could there be different port timing even though the CID is the same? It seems unlikely to me that only jetting would solve it as it may run rich??

 

[ODDD1]

Re: need help with my 115 hp Merc - please!

np....easy way is go to dealer and BUY a 125!

 

[nbpbborg]

Re: need help with my 115 hp Merc - please!

ODDD - if only it were easy to just "pick" money off a tree and drop 10 grand on 10 more horses. Many time we all fall prey to marketing tactics from corporations. My attemp is to find out just that. Was the 115 jetted up at a cost of 50 cents to Merc, or did they redesign a whole new motor from scrath, investing lots of R&D dollars? I believe the earlier, but that is why I am here for help. Yes, ODDD I could buy one. I could also buy a 175 EFI. I think you misse dthe point, or don't care to truley help someone who posted because they have a true need.

 

[Little Bear]

Re: need help with my 115 hp Merc - please!

nbpbborg,<br />I want to do the same thing. I own an 89' 100hp Merc and would like to change it to a 115 or more. Corm is very knowledgeable about this topic.<br />ODDD1 must have a pocket full of money, maybe he will buy us each a new motor of our choice. I WANT A 125HP MERC OR A 130HP YAMAHA. I have been a good little boy this year!<br />Best of Luck,<br />Little Bear

 

[nbpbborg]

Re: need help with my 115 hp Merc - please!

Little Bear:<br /><br />I am pretty sure your 100 to 115 is a carb issue only. I think you would need to pick up some used 115 carb which are higher CFM and jet size.<br /><br />My case is unsure since the 125 Merc is relatively new all anyone seems to know ith the CID and gearbox is the same. Good luck!!

 

[freddie]

Re: need help with my 115 hp Merc - please!

If you know the lower unit gear ratio and housing are the same ,than it's probably in carburation.Not just jetting,i'm talking the actual Bore size of the carb.I do not believe the port timing is different ,but I could be wrong.Hope this helps some.

 

[nbpbborg]

Re: need help with my 115 hp Merc - please!

Thanks Freddie -<br /><br />Do you or anyone else know where I can get this info from Merc?? Will they give it to me?

 

[Mozart]

Re: need help with my 115 hp Merc - please!

I asked the same thing (115 Horse Johnson / 125 Horse Johnson) some time ago when getting a motor serviced. It is partially in the jetting, also it has to do with the intake and exhaust - being tuned, ported and polished .... as per the mechanic. Also - check the coast guard plaque in the boat - usually your insurance is not any good, among other things, if you exceed the recommended HP for your boat.<br /><br />The mechanic that passed on this information also thought it was not economical (at least on an older boat) to try to increase the HP by this method as even from the factory, results may vary.

 

[Mozart]

Re: need help with my 115 hp Merc - please!

I asked the same thing (115 Horse Johnson / 125 Horse Johnson) some time ago when getting a motor serviced. It is partially in the jetting, also it has to do with the intake and exhaust - being tuned, ported and polished .... as per the mechanic. Also - check the coast guard plaque in the boat - usually your insurance is not any good, among other things, if you exceed the recommended HP for your boat.<br /><br />The mechanic that passed on this information also thought it was not economical (at least on an older boat) to try to increase the HP by this method as even from the factory, results may vary.

 

[Mozart]

Re: need help with my 115 hp Merc - please!

Hmm, didn't see my first reply.....<br />Block is the same for the engine, but intake and exhausts are different - they are "tuned" and also (I believe) polished. This in addition to the Carbs being jetted differently. My mechanic said is usually not cost effective to try and do this, as the gain is usually not that noticable - more of a marketing hype/persuasion from the manufacturer. (IMHO) as told to me by my Outboard mechanic.

 

[ol''joe]

Re: need help with my 115 hp Merc - please!

Crom told me one time that my 90hp merc inline 6 is a detuned 150. If I had the money. Port timing carbs ect. He would the one to contact.

 

[nbpbborg]

Re: need help with my 115 hp Merc - please!

After hearing most of this, I am inclined to believe it is carb bore size with jetting also. I still can't believe that polishing a port would give you 10 horses...but I have been wrong before!!

 

[ODDD1]

Re: need help with my 115 hp Merc - please!

Sorry, np..didnt want you to get upset...just yankin yer chain.....I hear 'the question' many times a week....can you make my 9.9 a 15 or my 75 into a 90 or my 100 into a 125....sure I can do every one of them, but does any body wanta pay for it? take your motor for instance...could be the same CID [didnt check] merc made the 4 cyl block in 3 3/8 bore or 3 1/2 bore hence the displacement discrepancy....can you make the HP with either bore size? you bet. what else? Carb/induction.. will amain jet change do it? maybe..merc uses different carbs between the 2 motors...would they do it if they didnt have to? nope. Reeds? merc changes thickness on lower hp lower rpm motors of same displacement...so maybe.<br />exhaust tuning? nuther maybe..gotta go by serial# an see if they changed tuners.....how about WOT rpm? sometimes we buzz em higher too...on the 4 cyl motor is not a good thing....5250 max to keep the crankshaft in one peice....and if you are gonna spin it faster you need an increase in timing too.....<br />My point is...if you go thru all this trouble an expense the cost at initial purchase between what you have and want you want IS A WASH..... perhaps you are even going backwards a bit when you consider you now have an "oddball" motor....one that whenever it is taken for service explaining will be done,assumptions will be made an when it changes owner, nobody down the road will know quite what it is.....I dont have any more money than you.....Ijust hate seein people make their lives more difficult...boating is supposed to be fun....

 

[freddie]

Re: need help with my 115 hp Merc - please!

vrey well put oddd1,very well put!

 

[JB]

Re: need help with my 115 hp Merc - please!

Hey, gentlemen. ODDD1 is spot on about the many subtle ways that these engines differ, and that it is almost never cost effective to convert one to the other. Why? The simple answer is corm's favorite formula: cubic inches=power.<br /><br />Horsepower ratings are a very good way to predict what and engine will cost, but only a fair way to predict how a boat will perform with that engine, assuming perfect propping.<br /><br />Engineers have looked for years for a more useful way to rate engines. Average torque x peak rpm, average (torque x rpm), peak torque, etc., etc. Marketers wont go for it. They want a big, simple number.<br /><br />The perfect outboard engine would have an amount of torque. . . .use 1 pound-foot per cubic inch as a f'rinstance . . . at idle, low rpm, high rpm and peak rpm. It would be geared to spin a perfect (no slip, no drag) prop matched to the boat it is on.<br /><br />None of them are perfect, but the best of them are the ones that come closest to that ideal: a very wide, very flat torque vs. rpm curve up to a high rpm. Horsepower ratings are incidental, and hopping an engine up usually changes the shape of the torque curve more than it changes anything else.<br /><br />Leave them as the engineers designed them. If you truly want better performance from a given engine, improve your hull drag, prop selection and balance. You will get a better return on your hard-earned bux.<br /><br />Happy Boating.<br />JB

 

[nbpbborg]

Re: need help with my 115 hp Merc - please!

Thanks all for the input - she's stayin' put.<br /><br />PS - Next time I buy a boat I am opting for the max rated motor from the get go - sometimes lessons learned best are the ones learned the hardest.

 

[sho305]

Re: need help with my 115 hp Merc - please!

Some motors are similar, you can find shops on the net that will convert newer v-6 to higher hp for $2k or so. It depends on the motor you have. Some big merc inline6's were the same cubic inch and had changes in port timing and carbs. If you are in the same motor family, you may be able to change it over. Need to find out what you have and find someone who does it, if the ports are bolt in or not, etc. Either way, you have to be the type that likes to mess with things you know? If not, forget it or pay for it. <br /><br />The factory will discurage this of course, and for example: a lower hp motor the same displacement will work much better on a heavier boat due to its greater low rpm torque, and will perform better! So there is reason for this, not just the factory digging in your pocket. Speed costs $$$

 

[skier]

Re: need help with my 115 hp Merc - please!

Y'all have overlooked one way to do this. Take my baot f'rinstance.<br /><br />I ahve a Glastron GS160 that is rated for a 120hp. Mercury doesn't make a 120hp engine and never has. I got a 1979 Mercury 115hp inline 6 (Not at the same place I got the boat). I was talking to a mechanic about upgrading to a Merc 140hp inline 6. He had a 1979 Mercury 140 in his shop and said that it would cost $2900.00 to install that engine or $800.00 to take the 140 powerhead and install it on my 115 leg. Everything matched up and it was 8 or so bolts, connecting the electrical, fuel, and throttle and gear and I had a 140hp. It took less than a day and I was back on the water.<br /><br />I hope this has given y'all a better way to upgrade your HP.<br /><br />Craig