Mercury tower of power HP question

[archbuilder]

Can anyone tell me what the difference is between the 115, 135, and 150 inline 6's? It looks like the same power head to me. What accounts for the HP difference? Reeds, jetting or is the displacement different?

 

[Texasmark]

Re: Mercury tower of power HP question

Most towers after the '60's initiation in white, used a 99 cu in block and yes at the end, just before the advent of the V's they got 150 hp out of 99 cu in. Additionally, I think Merc prop rated all those years which is one reason Merc used to whip the competition hands down who rated hp at the powerhead till the '80's.

To get 1.5 hp per cu in, they had to do some cute things, but they did: ignition, carbs, intakes, porting, reeds, timing and all that stuff.....yes you are right on.

I wasn't involved in the process then, but I followed it somewhat beins that I left OMC (as a consumer only) in favor of Merc back in the '70's when I got tired of Merc 125's whipping my Johnson 125's arse all over the place. Haven't looked back and haven't been sorry.

Best I can do.

Mark

 

[archbuilder]

Re: Mercury tower of power HP question

Thanks for the info Mark. I had heard they "underrated" them....we had a 115 back in the 80's on a deck boat.....and even on that heavy boat, hang on to your ***, it came out of the hole like a Saturn V rocket! I can't wait to see what the little ski boat I'm restoring will do with one on the stern!

 

[Texasmark]

Re: Mercury tower of power HP question

Like I said, it could be where they are rated. Also, engines are built to exceed hp ratings so that they can pass production minimum limits. No telling where the top end is.

Back when I was a kid using tiller small motors on rental boats, hp per hp, if there was a Merc around it was "Boss Hog". Grin.

Mark

 

[Chris1956]

Re: Mercury tower of power HP question

Arch, The late model ('76-'77) Merc 1500s had power ported pistons and radical timing, which boosted the HP over the 1150 motors. Other than that they were very close in design.

The earlier 135HP models achieved their power boost in other ways. There is a nice tutorial about the "History of Merc Inlines", which you might like to search up.

 

[archbuilder]

Re: Mercury tower of power HP question

Thanks I will look that up.

 

[archbuilder]

Re: Mercury tower of power HP question

Arch, The late model ('76-'77) Merc 1500s had power ported pistons and radical timing, which boosted the HP over the 1150 motors. Other than that they were very close in design.

The earlier 135HP models achieved their power boost in other ways. There is a nice tutorial about the "History of Merc Inlines", which you might like to search up.

Is the history of merc inlines on Iboats? I couldn't seem to find it. Thanks!

 

[Chris1956]

Re: Mercury tower of power HP question

Arch, I was unable to find it as well. I had thought it was posted on this site....

 

[OldMercsRule]

Re: Mercury tower of power HP question

Hey Fellers,

The history of inlines is on Scream n' Fly.

Mark is a bit wrong about the prop rating issue. Merc always underated their inline6s. That said: they did rate them at the crank 'til 1982 when they rated them at the wheel, (prop).

He is correct in that they were always underated vs other manufacturers. It was most dramatic in the 1950s butt: corntinued to the last year of the inline6s: 1988. Dunno 'bout the newer stuff.

The first production manufactured 100 HP engine, (also the first time Karl painted the VERY purdy ol' girls Black), was a very purdy 89.x cubic inch inline6 that was made from 1962 to 1969, (in 1967 they called it a 950) to differintuate a bit from the 94.x 110 HP engine.

The first 99.x cubic inch inline6 was the 1968 125 HP 1250, and after the 1969 model year all of 'em were 99.x cubic inches from the 90HP 900 to the 150 HP 1500. In 1970 they changed the 1250 block, (although still a "silver block") to the 1350 and the 1150, (it is fairly easy to make a 1970-72 1150 a 1350 with reeds n' minor mods to the carbs), THE ONLY TIME in the inline6 lineup you can make a modest change to increase HP, (the rest are best left alone as the factory was obsessed with testing and ya can't beat Karl at his best game).

Once Merc went with a bigger cubic inch v-6 they renamed the 1500 a 140, to differentuate from the 150 HP v-6.

In 1982 they went to prop ratings and the ol' 1981 140 was a 1982 115 and the ol' 1981 115 was a 1982 90.

The prop rated 1982 115 had less flow at the reeds then the ol' 1500 or the 140 so it had somewhat less HP. The difference between an 1982 90 and a 1981 115 is less clear ta me as I have not had those two apart n' I only have one functional brain cell.

I hope Ed from Pauslbo, Chris1956, or Laddies or some of the other big guns here on iboats will chime in ta tell us what the difference was between the 1981 115 and the 1982 90 as 25 HP is far more then the 8% to 13% difference from the crankshaft to the propeller.

Me overpriced $.02. JR

 

[Texasmark]

Re: Mercury tower of power HP question

Thanks Old Mercs for setting that straight. Like I said I was just WAGGING.

However, having had one of those 115's of '89 vintage, when did that engine get the Direct Charge enhancement? Mine had it and I just loved it.

Thanks,

Mark

 

[OldMercsRule]

Re: Mercury tower of power HP question

Thanks Old Mercs for setting that straight. Like I said I was just WAGGING.

However, having had one of those 115's of '89 vintage, when did that engine get the Direct Charge enhancement? Mine had it and I just loved it.

Thanks,

Mark

Mark,

Are ya sure yer Tower was an 1989? Me thinks 1988 was the last year fer the inline6....... sniff sniff, (I could be wrong), only one functional brain cell.

The "Direct Charge" first came out in cornsumer inline6s in 1970 with the 1350 n' the 1150 silver blocks.

I read somewhere that the 1969 1250 BP has the Direct Charge as well. (Dunno as I have never owned one).

Both me 1968 1250s are the earlier 99.x cubic inch models.

I own a parts 1971 1150 Silver Block n' a sweet fresh water virgin 1972 1150 Silver Block, both say "Direct Charge" on 'em that the 1250s do not say.

Respectfully, JR

 

[madgadget]

Re: Mercury tower of power HP question

Not really to add anything value I'm afraid, but I just had to chime in and say that this year with my first boat a 16foot fletcher gto, the first ever OB engine I experienced on it was a 79' I6 140. Man does it shift. Just hearing you lot talk about them makes me excited haha I love that engine...

 

[archbuilder]

Re: Mercury tower of power HP question

Thanks for all the info, I should have a 86 115 for my restoration project in a week or two....can't wait to get it strapped on to the back of my 16' ski boat and hang on!

 

[Droll]

Re: Mercury tower of power HP question

Are ya sure yer Tower was an 1989? Me thinks 1988 was the last year fer the inline6....... sniff sniff, (I could be wrong), only one functional brain cell.

Last production year was 1988, but ...

The "Direct Charge" first came out in cornsumer inline6s in 1970 with the 1350 n' the 1150 silver blocks.

The first DC engine was the 4 cylinder 1969 Merc800

I read somewhere that the 1969 1250 BP has the Direct Charge as well. (Dunno as I have never owned one).

The 1969 Merc1250 was a crossflow engine but at the time they also made a Merc1250 SUPER BP THIS one was a DC engine ( Prototype )

I own a parts 1971 1150 Silver Block n' a sweet fresh water virgin 1972 1150 Silver Block, both say "Direct Charge" on 'em that the 1250s do not say.

DC engines ( highlights ):

• 1969 Merc800, production engine
• 1969 Merc1250 SUPER BP ( prototype with a blue printed engine )
• 1970 Merc1150/Merc1350
• 1972 Merc1400 ( basically the same engine as the 135 but with exhaust tuning and a new bolt pattern between block and leg )
• 1973 Merc1500 ( basically the same block as the 140hp but with the addition of "power ports"
• 1973 ALL inline 6 engines got the new bolt pattern between leg and block .
• 1978 The previous 150 inline 6 engine gets new decals saying 140hp ( NO other differences )
• 1978 First year of the Merc1500XS ( 155hp, short shaft, lwp lower unit )
• 1979,5 ( mid 79 ) Switched from Dist. to ADI ignition.
• 1982 Mercury start measuring the engine hp at the propeller, then 140hp becomes 115hp ( ARE some other minor difference too ), Mercury 115 hp engines ABOVE serial 5829464 are rated at the propeller.
• 1984 New power trim unit, integrated as used on the V6 engines .
• 1988 Last production year of the inline 6 DC engine .

Arne Kjetil

 

[OldMercsRule]

Re: Mercury tower of power HP question

Last production year was 1988, but ...



The first DC engine was the 4 cylinder 1969 Merc800



The 1969 Merc1250 was a crossflow engine but at the time they also made a Merc1250 SUPER BP THIS one was a DC engine ( Prototype )



DC engines ( highlights ):

• 1969 Merc800, production engine
• 1969 Merc1250 SUPER BP ( prototype with a blue printed engine )
• 1970 Merc1150/Merc1350
• 1972 Merc1400 ( basically the same engine as the 135 but with exhaust tuning and a new bolt pattern between block and leg )
• 1973 Merc1500 ( basically the same block as the 140hp but with the addition of "power ports"
• 1973 ALL inline 6 engines got the new bolt pattern between leg and block .
• 1978 The previous 150 inline 6 engine gets new decals saying 140hp ( NO other differences )
• 1978 First year of the Merc1500XS ( 155hp, short shaft, lwp lower unit )
• 1979,5 ( mid 79 ) Switched from Dist. to ADI ignition.
• 1982 Mercury start measuring the engine hp at the propeller, then 140hp becomes 115hp ( ARE some other minor difference too ), Mercury 115 hp engines ABOVE serial 5829464 are rated at the propeller.
• 1984 New power trim unit, integrated as used on the V6 engines .
• 1988 Last production year of the inline 6 DC engine .

Arne Kjetil

Thanks Arne.

What about the 1981 115 and the 1982 90? Were they the same or did they detune the 115 as the did with the 1981 140, (reeds) ta make the 1982 115???

25 HP is not lost in the gears!!!!

JR

 

[Droll]

Re: Mercury tower of power HP question

Thanks Arne.

What about the 1981 115 and the 1982 90? Were they the same or did they detune the 115 as the did with the 1981 140,

Serial No. 5299506 and Above was rated at the propshaft ( 90hp ), so the pre 82 115hp became 90hp.
I would assume the 115/90 was identical inside .

1981 140 (reeds) ta make the 1982 115???
25 HP is not lost in the gears!!!!

Well the story start with the older 150hp engine as it's identical with the later 140hp ....
Some of the changes were:

• New low dome pistons from around 1978 .
• New reedbock design ( 10/8 reeds ), was to even the gas/fuel mix to the cylinders ( 10 holes up and 8 holes down, gravity helped the 8 hole side so it had the same air/fuel flow as the 10 hole side)
  ( Used different type of reeds too, 10 hole side used the 150hp type reeds, and the 8 hole side used the older 115hp type of reeds )
• Some of the first prop rated 115hp had the same block as the earlier 140hp engine ( a bit stronger at the top ), but as soon the remaining stock was used they started to use a "new" 115hp block ( got a slightly lowered exhaust port, like 0.020" lower ), this gave the later 115 a bit more low end power.

The later engines used a more modern type of rods too... not exactly sure how they contributed to the output, they were considerably lighter than the earlier bolt/nut type ...

Reed block designs

Bigger picture

Reeds design

Banjo reeds as used on the 10 hole side on the late 115 and bout sides on the earlier 150/140 and the 155hp XS.

Used on the early 140hp ( 1972 ) + the early 115 hp + the late 90hp + on the 8 hole side on the late 115hp .

Rod design

Bigger picture




Arne Kjetil

 

[archbuilder]

Re: Mercury tower of power HP question

So my 86 is really one of the most refined of the series. From what I'm reading it was also one of the models with the most horsepower due to the shaft rating. How will it tolerate lower octane unleaded fuels? I plan of avoiding alcohol base fuels like the plague!

 

[Droll]

Re: Mercury tower of power HP question

So my 86 is really one of the most refined of the series. From what I'm reading it was also one of the models with the most horsepower due to the shaft rating.

Well the earlier Merc1500 and Merc1500XS had more horsepower, your engine got less top end hp but in exchange you got more torque and reliability .
To compare the output on the older engine.... my guess would be 130 > 135hp ( prop rated ) on the earlier 150 and 155 hp engines .

The earlier high hp models needed good high octane quality fuel, with the porer quality fuel on the marked from mid 70s up to today Mercury had to make some adjustments to the engines to keep them from burning pistons....

First steep was to lower the compression a bit ( low dome pistons ) + lower the max ignition advance down to 20 > 21 degrees.


In short... you got LESS hp on top, but you got more hp and torque at lower rpm ( better holeshot, better for water sport )...

The later models got lots of improvement over the years...

• The 150 used distributor ignition, later engines used ADI ignition ( from mid 79 )
• Earlier models used external powertrim cylinders with a oil pump mounted inside the boat... later modies ( 84 > ) got an integrated unit.
• The starting system evolved from choke flaps to fuel "injectors" ( early 80s ? )
• Gearhousing, later models came with a more streamlined lower unit ( backsweeped skeg ) came around early 80s .

Those engines evolved a lot, you got one of the top evolved.

How will it tolerate lower octane unleaded fuels?

2-storke engines doesn't need any lead so that's no problem...

From Mercury...

FUEL RATINGS
Mercury Marine engines will operate satisfactorily when using a major brand of unleaded
gasoline meeting the following specifications:

USA and Canada - having a posted pump Octane Rating of 87 (R+M)/2 minimum.
Premium gasoline [92 (R+M)/2 Octane] is also acceptable. Do NOT use leaded gasoline.

Outside USA and Canada - having a posted pump Octane Rating of 90 RON minimum.
Premium gasoline (98 RON) is also acceptable.

NOTE: Some Hi-performance engines require a higher octane fuel.

Others might comment on this one ...


Arne Kjetil

 

[OldMercsRule]

Re: Mercury tower of power HP question

Droll stated:

Well the earlier Merc1500 and Merc1500XS had more horsepower, your engine got less top end hp but in exchange you got more torque and reliability .
To compare the output on the older engine.... my guess would be 130 > 135hp ( prop rated ) on the earlier 150 and 155 hp engines .

If ya loose 13% the 1500 would be 130.5 n' the XS would be 134.9; if ya loose 8% 138 n' 142.6 respectively. As Mark in Texas said: Mercury underated their inline6s relative to other engines of the era, (or any era fer that matter).

The earlier high hp models needed good high octane quality fuel, with the porer quality fuel on the marked from mid 70s up to today Mercury had to make some adjustments to the engines to keep them from burning pistons....

First steep was to lower the compression a bit ( low dome pistons ) + lower the max ignition advance down to 20 > 21 degrees.

When I rebuilt me 1976 1500, (the only inline6 I ever rebuilt), I put the 140 (slightly lower dome) pistons in her.

In short... you got LESS hp on top, but you got more hp and torque at lower rpm ( better holeshot, better for water sport )...

Yup, I had a real sweet 1968 1250 short shaft, (now a parts engine), that ran fer many many years n' many many hours, (the reason I fell in luv with the Merc inline6). Yer 1986 115 would be very similer in power output to the 1250, (maybe a little hotter), butt likely a bit less then the 1350. My 1250 was the most powerful outa the hole of all me inline6s, butt: the purdy ol' girl did suck more fuel then yer 1986 115 does, (non direct charge), n' direct charge did improve fuel economy.

The later models got lots of improvement over the years...

• The 150 used distributor ignition, later engines used ADI ignition ( from mid 79 )
• Earlier models used external powertrim cylinders with a oil pump mounted inside the boat... later modies ( 84 > ) got an integrated unit.
• The starting system evolved from choke flaps to fuel "injectors" ( early 80s ? )
• Gearhousing, later models came with a more streamlined lower unit ( backsweeped skeg ) came around early 80s .

Correction: the more streamlined gear case (with the pedo pick up) n' a wee bit more gear oil came in 1978 on the inline4(s); n' 1979 on the inline6(s)

Those engines evolved a lot, you got one of the top evolved.



2-storke engines doesn't need any lead so that's no problem...

From Mercury...

Others might comment on this one ...

Yup, all ya need is 89 octain, (hopefully non E-10), fresh fuel with the max timin' set as Arne jus' said.


Arne Kjetil

Me overpriced $.02. JR

 

[Droll]

Re: Mercury tower of power HP question

• Gearhousing, later models came with a more streamlined lower unit ( backsweeped skeg ) came around early 80s .

Correction: the more streamlined gear case (with the pedo pick up) n' a wee bit more gear oil came in 1978 on the inline4(s); n' 1979 on the inline6(s)

But I was close , the extra oil would be to compensate for the bearing they removed ? ( reverse gear )

When I rebuilt me 1976 1500, (the only inline6 I ever rebuilt), I put the 140 (slightly lower dome) pistons in her.

Have use high dome in all my engines, no problems doing so but it needs the proper gas/timing and WOT setup...

Got 6 new HD pistons on the bench now for my winter project

Arne Kjetil