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  1. #1

    Default Which is better: 1988 Mercury 100 HP or 1991 Mercury 115 HP?

    I am looking into purchasing a boat for the first time and am looking at two 16 foot Starcraft Medalist boats. One has a 1988 100 HP outboard and the other has a 1991 115 HP outboard. I was told that the 115 HP would go through fuel more quickly than the 100 HP. Is this true? I understand that it depends on many factors, but want to know if there is a big difference in the efficiency of the motors. I would appreciate any help in this area. I am planning to use the boat on small lakes for skiing and tubing.

    Thank you,
    Shawn

  2. #2
    Join Date
    Nov 2011
    Location
    tennessee
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    4,877

    Default Re: Which is better: 1988 Mercury 100 HP or 1991 Mercury 115 HP?

    These are the same exact motors and the only difference is the carbs, the 115hp will use less fuel at as the 100hp will work harder at the same speed.

  3. #3

    Default Re: Which is better: 1988 Mercury 100 HP or 1991 Mercury 115 HP?

    Thank you for answering my question so quickly!

  4. #4

    Default Re: Which is better: 1988 Mercury 100 HP or 1991 Mercury 115 HP?

    I know really old thread sorry. But I have a 1988 merc 100. I have had some people say that changing the carbs will make it 115 hp. Then some say no I will just waste my money and it will flood out. Ideas?

  5. #5
    Join Date
    May 2013
    Location
    TX.
    Posts
    549

    Default Re: Which is better: 1988 Mercury 100 HP or 1991 Mercury 115 HP?

    I bought a new Ranger bass boat with a 115 HP 6 cylinder "Tower of Power" in 1989...on the title listed as a 1989 engine. Folks in the know on here said that Merc. did the change over in 1988.......sooooo I guess I had an engine built in '88 and marketed in '89, not an unusual process. The engine was "Direct Charged" and was Merc's intermediate solution to the OMC Loopers which were known for their fuel economy over their previous "cross flow" conventional scavenging engines....which loved to stop by the gas station....BTDT

    Out comes the new Loop Charged Mercs in 1989, 3 and 4 cylinder, 60 HP Jet 3 cyl to 125 HP 4 cyl. Later on I bought a 115 hp one of these engines. I remember the '89 was very fuel efficient as is the current 2002 115. I can't recall that fuel was an issue worth mentioning with either. Do I have a preference? Well, it's hard to beat a 2 stroke 6 cylinder engine of any type for smoothness of idle.....like a well oiled Singer Sewing Machine. But the current 4 cylinder, which runs on 2 cylinders at low speeds is very smooth....as long as you tilt the back of the engine up 10-15*. Otherwise it wiggles a bit.

    To answer your question, I'd say noise would be the big difference as the newer engines had a foam insulated one piece, plastic cover, very effective noise canceller, where as the inline 6 had a wrap around cowl with a plastic bag of loose fiberglass for sound deadening. Course when it was making the most noise, it was going the fastest, which it did very well and most of the sound was way behind the boat.

    Also the lower unit was beefier, I don't recall the '89 being thermostatically controlled, and the improved trim setup did a better job of allowing the engine to raise up when hitting an obstruction, reducing damage to the LU.....the trim ram was separate and just pushed up against the mid section rather than being a single cylinder for trim and tilt, locking the midsection to the hydraulic pressure of the TT unit at the time of impact.....as I recall on the '89. I recall an earlier Merc 850 I had with the same trim and one day I ran over a concrete anchor to a marina. Rear of the boat raised and fell as I passed over it.....don't recall any noticeable movement of the engine. Upon loading the boat on the trailer to go home, I noticed that the lower part of the skeg was missing...just sheared right off.
    Last edited by Texasmark; 01-20-2021 at 08:54 AM.

  6. #6
    Join Date
    Sep 2010
    Posts
    21,194

    Default Re: Which is better: 1988 Mercury 100 HP or 1991 Mercury 115 HP?

    The ---" direct charge " ----Is not much different than ---" crossflow " ----as far as scavenging the cylinder.-----Marketing 101 says that most folks have no clue on internal working of a 2 stroke.----You can fool them with this terminology.

  7. #7
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    4,877

    Default Re: Which is better: 1988 Mercury 100 HP or 1991 Mercury 115 HP?

    The 1988-1993 are all small bore 105 CID motors and the 1994 and up are big bore 113 CID motors. If you can find a set off a pre 1993 motor it will work...
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  8. #8
    Join Date
    May 2013
    Location
    TX.
    Posts
    549

    Default Re: Which is better: 1988 Mercury 100 HP or 1991 Mercury 115 HP?

    Quote Originally Posted by faztbullet View Post
    The 1988-1993 are all small bore 105 CID motors and the 1994 and up are big bore 113 CID motors. If you can find a set off a pre 1993 motor it will work...
    Interesting. Being of a curious nature, what else was different in the engines for a given HP....RPM max rating changed? Carb jets? Reeds? Porting? I guess, like their 2k vs 2.5k Bass boat V engines, better hole shot with more cubes?

  9. #9

    Default Re: Which is better: 1988 Mercury 100 HP or 1991 Mercury 115 HP?

    I found a set of 115 hp carbs but I dont know the year. There is a number on the carb 3301-9012Click image for larger version. 

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  10. #10
    Join Date
    Jul 2020
    Location
    Western Australia
    Posts
    63

    Default Re: Which is better: 1988 Mercury 100 HP or 1991 Mercury 115 HP?

    When it comes to part numbers i just punch them into my search bar and it usually tells me what i need to know hope this helps good luck

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