TOPIC: HP increase for the inline 115 Merc

Guys,
I've read that you can use older Merc 135 components to increase HP on an older Merc 115 inline. Question, can you do the same (using an older 135) to increase the HP on a newer 82 model 115 merc? Does it even make sense i.e increase to efforts?

Thanks
Robert

Depends on your 115. If its the propshaft rated 115 then its just about as good as it can be. If its the older 115 then possible.

I think the change happened in 1982. The 115 could be either the old or new style.
Conrad

Old 115's are 135's, with some flow restrictive stuff, exhaust tuner, reeds, carbs, Thom built me one back to 135, from a 72, 115.
On the newer 115's, probably a different animal, than one 10 years before. You could do a parts number search, certain stuff, both, but a lot of work, and I really don't think worth the effort.

Conrad, here is a chart that shows some of the differences. You are correct they changed in 82 to prop rated.

Dave cool chart. What do your A,B,C etc porting specs mean? Or is it irrelevant your just showing the ones with the same?

Conrad

Nice chart Dave! copied..thanks!

They are irrelevant, just convenient grouping for port maps that have the same dimensions. Arne Kjetel put this together when he was researching port maps. I just knew where to find it.

Thanks Guys,
I appriciate the help and advise.

Thanks
Robert

Hey, Robert, I dug thru my archives and found some info that might help:

"Mercury 115 hp engines ABOVE serial 5829464 are rated at the propeller"

So, if yours meets that criteria, you've got a 115hp power-ported motor that used to be rated at approx. 140hp at the crank.

My understanding was the biggest diff between the later-model 140 and the older 1500 motors was the newer motors used Low-dome pistons in a quest to reduce engine destruction from detonation (as a result of declining fuel quality).

The 1500's used Hi-Domes, more spark advance and may have been ported a bit more radical as well. Guess I need to study that chart a bit. Maybe when my eyeballs get un-dilated (just had eye exam today, everything is SO Bright and Shiny!!).

Thom (aka the Good Dr. FrankenMerc) built a pretty stout piston-ported ADI Six using Hi-Domes, older 10-petal reed blocks, and 1500 carbs. I can testify it's a head-snapper!

So, if your 115 is the later-production power-ported motor, she's a strong runner already. You can do stuff to "tweak" it up a bit, but mostly you'll gain hi-end performance and will be needing to run hi-octane fuel or 100 L/L Avgas if you can get it.

If you have an earlier 115 block, that's what became the "90" after the change from crank-rated to prop-rated hp.

In that case, the most economical way get more power would be to pick up an ADI power-ported block (or complete powerhead). If you found only a block, your 115's entire rotating assembly (less pistons) could be swapped over, with the addition of a new set of power-ported pistons.

I imagine you could just rejet your existing carbs, since as far as I know all the Big Six carbs throats are the same i.d.

Anyway, hope that helps in your quest for more speed.........ed

So, the short answer is no. The 1350 is basiclly a non powerport 1500 on a slightly different midsection and exhaust tuning, the intake ports are tall, like a 1500. If you have a NON powerported 1150, (that would be with a distributor), intake ports are machined the same way as a 1500 but are shorter, this is the limitation to HP on a 1150 and is not really a bolt on swap with 1350 parts to increaase HP, unless you have same year 1150 and want to swap on a 1350 block and get a set of 1350 carbs or carbs will interchange but rejetting is needed the throat size is similar so no HP is to be found there.
If you have a powerported 1150 then forget the 1350, anything you do will reduce HP of that version 1150, it already makes more power than the 1350.
The history is like this:
70,71, 1150 and 1350 are direct charge, same block, ported different on intake side and carbs jetted different. Blocks are silver.
Mid section tuning changed in 72 1350 becomes 1400. 1150 does not really change. Again carbs similar but jetted different. Blocks are now black.
In 73 powerport added to 1400 and becomes 1500. 1150 not really changed.
1500 remains unchanged for 75 and 76. 1150 remains basicly unchannged during these years. Timing gets reduced to 21 total on 1500 from 23 as detonation starts to show up frequently on these, not as big an issue on the 1150 which was timed at 21 anyways.
Around 77 the 1500 inline becomes a 1400 by putting low dome pistons in, again response to detonmation issues, porting unchanged. 1150 stays essentially the same. I am not sure if they swapped to low dome pistons int the 1150 at this time.
Early in the 80's ADI replaces the distributor and the HP is rated at the propshaft rather than flywheel on older motors.
1400 becomes the "new" 1150 and the 1150 becomes the "new" 900.
So in the final years the 1150 is a lowdome distributorless version of the earlier 1500 and ditto for the 900 being a possible low dome but, definitely distributorless version of the earlier 1150. Lots of stuff transfers from 73 up to the end years.
Dr. Frankenmerc built the ultimate pedestrian inline with
power ported high domes (early 1500) in an ADI powerported block (late 1150) It would create a 1500 with a much better ignition system than the belt driven distributor.
Randy

Randy,

70,71, 1150 and 1350 are direct charge, same block, ported different on intake side and carbs jetted different. Blocks are silver.

From what I have learned the 1150 and 1350 shared the same block during 70-71. Only diff is carb reed stop height and exhaust plate.

If yo had a bare block on the bench you could not tell them apart.
Conrad

Conrad is correct on the early 1150/1350 blocks, the intake & exhaust port sizes are the same for both.

The 1150 carbs had a larger plastic venturi in their throats, and smaller main jets. If you swap out the jets and venturis for 1350 bits, & add the larger reed stops & exhaust plate, you've got a 1350.

Cheers........ed

Well then I stand corrected. Merc must have shrunk the ports on the 1150 after those years to reduce HP instead of restricting/detuning as it sounds they did in 70/71. That smaller carb/reed height/exhaust plate recipe is how the made a 1000 vs 850 from the same blocks in the earlier 60's so I guess they went with that idea on the first gen direct charge motors. THANKS for that info!
Randy