How to upgrade the Merc 115 straight 6???

[Graham C]

As the title suggests... I'm looking to see if the power can be hiked from a late 70's early 80's Merc 115 straight 6. I am led to believe this lump has varying outputs of 90-140bhp!? Is there any truth in it and what are the differences?<br /><br />Cheers<br /><br />Graham

 

[Chris1956]

Re: How to upgrade the Merc 115 straight 6???

Graham, The Merc inline sixes had power ratings from 90-150 HP (at the flywheel). From what I understand, they share displacement but have different porting, some have different pistons and carb jets. The 150 HP IL6 also has the piston with the power port, as does the later 115HP models. To boost the power on your 1150, you would need to have the ports modified, change pistons, carb jets etc, as a minumum.

 

[studlymandingo]

Re: How to upgrade the Merc 115 straight 6???

I have heard that rejetting the carbs can increase your HP.

 

[studlymandingo]

Re: How to upgrade the Merc 115 straight 6???

I have heard that rejetting the carbs can increase your HP a bit.

 

[studlymandingo]

Re: How to upgrade the Merc 115 straight 6???

I have heard that rejetting the carbs can increase your HP a bit.

 

[79Merc140]

Re: How to upgrade the Merc 115 straight 6???

Like Chriis said, They went up to 150hp at the cranksaft (Flywheel). The 150 as I understand it never really gave a full 150hp at the crank, so it was "Demoted" to a 140. In 1985/86, Mercury went to prop rated hp ratings and basically took the 140 and put 115 cowlings on it and called it a 115hp, which was closer to 120hp at the crank. The 90hp inline 6 was discontinued and made into a inline 3. There was a couple of years that an 1150 (115) could be made into a 1350 (135), just by changing the carbs and I think it was 71/72. there are threads on it. Just search for it.<br /><br />craig

 

[Clams Canino]

Re: How to upgrade the Merc 115 straight 6???

If it's true 115, nothing you can do. Carb jetting will do nothing. If it's a late (propshaft rated) 115 then using 1500 type reeds, pistons, and carbs will squeak another 5-10 hp out of it.<br /><br />All the 99ci inlines have about the same low end yank. The top ends are where the differences really show up. And there's something to be said for not running a 30 year old motor at the high end all the time.<br /><br />-W