85hp Merc?

[Chris1956]

Merc 650's were three-cylinder, two carb motors. The 50HP, 80HP and 85HP motors of that era were 4-cylinder, 2 carb models, if anyone cares.

 

[cesandroid]

Alot of good feedback on these motors..Thanks guys! So the motor is sold. Just like that.. hopefully the new owner got a good deal or maybe they have parts for it.

 

[Nordin]

Late 60es (68-69) and early 70es (70-71) 650 were 4 cylinders.
The 3 cylinder 650 was from 72-76.

 

[racerone]

The 3 cylinder was still produced after 76 as a 70 hp ( powerhead rated ) and later as a 50 or 60 prop rated.

 

[redneck joe]

The 3 cylinder was still produced after 76 as a 70 hp ( powerhead rated ) and later as a 50 or 60 prop rated.

Not to derail thread but this is close enough I think. On the ratings, I have an 82, 50 hp 4 cyl but also snagged an 87, 70 hp 3 cyl. So would there be any real increase in performance if I got the 70 running and swapped it?

 

[racerone]

I never really liked those 3 cylinder 2 carburetor motors.

 

[Chris1956]

The 70HP is a 40% increase in power, on paper. Those 50HP/4cyl were real good motors, such that Merc made it longer that one would expect, as they were really popular, and ran well. If the motor is 70HP/4 cylinders it may be real good as well. I have NOT heard (no direct experience) good things about the 3 cylinder, 2 carb 650 carb inline motors. from the mid 70's. Just what I have heard.

 

[jimmbo]

Not to derail thread but this is close enough I think. On the ratings, I have an 82, 50 hp 4 cyl but also snagged an 87, 70 hp 3 cyl. So would there be any real increase in performance if I got the 70 running and swapped it?

About 5-6 mph higher top speed

 

[jimmbo]

About 4-5 mph higher top speed

 

[redneck joe]

About 5-6 mph higher top speed

That's it? Any better hole shot?

 

[jimmbo]

Rule of Thumb for years has been 1 mph for every 5hp Increase. I also factored that your 50hp was Crank Rated, and the 70hp was likely Prop Rated. so I added a bit to the estimate. If both engines were rated the same way, the increase would be about 4 mph.

The 70 is a Larger Displacement, so it should have more Torque, and the Hole Shot will be a bit better. But a lot will still depend on how it is propped

 

[jimmbo]

deleted

 

[redneck joe]

Math works. At max rated hp that would put it an low to mid 40mph at wot.

Thanks, I can now calculate the cost of the beatings I would recieve in spending money on a bigger engine....

 

[Chris1956]

Gee, Don't the beatings continue until morale improves?

 

[airshot]

Grew up during late 50-60's era outboard motors, not sure I would go back that far for another motor, but I have been very impressed with my 1992 Merc 40 classic. Care and maintenance is everything and I found a good one. One of the smoothest running motors I have ever owned and can't believe how little fuel it really uses. I don't often run wot due to waves conditions on the big lake, so my typical speed is in that 3500- 4500 rpm range. Fuel economy has been impressive to me. Lots of improvements made in 80's and 90's from those early 60's models as far as quiet and performance.

 

[Texasmark]

Not to derail thread but this is close enough I think. On the ratings, I have an 82, 50 hp 4 cyl but also snagged an 87, 70 hp 3 cyl. So would there be any real increase in performance if I got the 70 running and swapped it?

The 3 cylinder is probably Loop Charged allowing for increased fuel economy. I will say this about my experiences with Cross Flow fueling methods vs Loop Charging methods......the CFs I owned were bullet proof and easy to start after sitting up between outings. My loopers not so.....a lot more picky....course they are made to run on less fuel so they are built that way.......and since fuel is what goes BANG in the combustion chamber, the. more fuel, the easier the bang.
I bought a new Johnson 125 CF back in 1972. Had it for about 8 years with the kids growing up. Went to the lake every week, sometimes twice. Water skiing was its main usage. Changed absolutely nothing on that engine.....nothing, impeller, surface gap spark plugs.....nothing....just put regular gas and OB oil in the tank and away we went....oh and gas was 35 cents a gallon.....I remember that.

On not knowing about worrying about impeller problems if you didn't religiously change it frequently, I used to slalom behind that boat and the engine had dual, round, exhaust relief ports in the top of the mid section and both would be full flowing water at around 30-35 MPH where I liked to ski.....didn't go faster because falls hurt too bad.......

 

[racerone]

The 3 cylinder 650 and 700 ( 72 to 1980's ) were crossflow ( direct charge ) as Mercury called it.----No reason for a crossflow or loop charge to be hard to start!

 

[Texasmark]

The 3 cylinder 650 and 700 ( 72 to 1980's ) were crossflow ( direct charge ) as Mercury called it.----No reason for a crossflow or loop charge to be hard to start!

Well I had the last 1988 (year built, sold as a '89 model) 115 I6, Direct Charged "Tower of Power" on my new 1989 Ranger Bass Boat. Absolutely one of the finest engines I ever owned. The DC engine had the domed piston like the CF, unlike the Loopers, but had a hole added to the side of the piston unlike the CF. Apparently that was a better entry point for fuel and made the engine efficiency more like the loopers rather than the gas loving CFs.....I think OMC still had the patent on Loop Charging causing Merc to opt for something else to improve fuel efficiency. I guess when the patent expired Merc could build their own Loopers. My 2002 115 4 cylinder was a looper.

I don't know all the details of the differences in the designs of the 3 engine types but there was absolutely nothing wrong with that DC engine. On my first outing, I was up at 55 MPH on my way on up when the Ranger started "chine walking".....scared me and shut her down. Was running a 24P Laser the dealer installed......didn't check the RPMs but they had to be low at that speed with a 24 prop on a 115 with a 2:1 gear ratio. Traded the prop in for a 19 or 21, forget which, and it would sit on 6k, kissing 50, and sing all day. You could trim it out till the prop was partially airborne...RPMs increased while the speed started falling off and hear the engine singing and the prop blades humming as they beat the water. Great sport.

This was my first experience with a "pad" boat and that was a new experience. I never had a boat come up out of the water like that and ride high and dry.

Being that the Laser (original design) was ported, (as is the Laser II of later years) you could hammer down in the hole shot, engine trim centered, get on plane fast and coming on up in speed as you were trimming on out, when the new water would seal off the ports, it was like shifting gears.....the boat would lurch forward with the new bite the prop had with the water......great sport. The other neat thing was that the same prop that got me 50 MPH also could pull me up on a Slalom ski without blinking with the ports doing their thing.

 

[jimmbo]

The Pistons in a DC Engine were a lot different than regular Crossflow

Direct Charge Piston(with Power Port)


Crossflow Piston