1977 vs 1983 johnson

[bcj.jones]

I have a 1989 bass tracker tx-17 rated for up to a 80 horse. It has a 50 on it now but with my in it, two batteries and 6 gallons of fuel plus normal light tackle I'm only get about 33 mph with a 17 pitch prop. So I'm looking for some more speed. I have two motors I found for a good price. One is a 1977 70 horse johnson and the other is a 1983 75 horse johnson. Is either one of them better then the other? Any known problems for either? As I understand it they ate both very reliable motors but want to make sure before buying one. I don't consider the loss of 5 horses to play a factor into the decision unless that motor is of lesser quality. Thanks for any help!

 

[RCO]

Either of those motors are crankshaft rated horsepower. If your 50 is an 89, it is prop rated. You would only be gaining 5-10 actual horsepower. You would probably get a noticeably better hole shot, but not a lot more top end.

 

[bcj.jones]

Gotcha! Thanks a lot! Coming from a kayak, everything boat related is new to me. I'm assuming at some year they started rating outboards at the prop instead of the crank? I'll Google that. Search continues for a motor then. I'll have to find out the year they started prop horsepower rating and find a 70-75 horse of those years. Thanks again man, helped me from wasting my time!

 

[racerone]

The 83 model 3 cylinder is by far a better motor.------The lower unit on the 89 model 50 is considered " flimsy " by those who know.

 

[bcj.jones]

Wait.. the loss between the crankshaft and the prop is around 15%??....that seems excessive..

 

[jimmbo]

If the hp loss sounds high, either the crank rating was a bit optimistic, or the prop rating is on the low side(makes for a better performing hp). Both engines are 49.7 cu in powerhead, which was introduced as a 55 hp in 68. Changes to pistons, additional transfer passages, and exhaust tuning yielded 60, 65, 70, and 75 hp versions. Prop rating dropped the engines back to 60 and 50hp models. I guess the 83 would have minor changes/improvements over the 77. The gear housings were slightly different shapes, and I assume timing specs were revised to deal with lower octane fuels

 

[flyingscott]

Go with the 1983 motor. The 77 probably does not have t/n/t and is very hard to find that style. The 83 May or May not have it if not it, can be put on fairly easily. The 75 Hp Motr Was Built Until 88/89 On The same Block. I Always Thought The 2/3 Cylinder Motors Were Pretty Strong Motors And Probably Pretty Close To a Prop Rating.

 

[bcj.jones]

Gotcha, so the 83 in your opinion is pretty close to 75 prop horsepower, even though it was rated at the crank?

Also, how much benefit it the 3rd cylinder. I also found a 1992 mercury 60 horse that's 3 cylinders for a smoking deal. Being that mine is a 50 horse 2 cylinder, the 10 horse difference is marginal but does that 3rd cylinder help over the 2 cylindee?

 

[flyingscott]

I would go with the newest possible motor I could afford. The 3rd cylinder does make difference in running quality they will usually idle smoother. The OMCs are not known for the idle quality.

 

[jimmbo]

The loop charging does make for a lumpier idle
There is a marked difference in the torque curve between the 70hp and 75hp. The 75 was really designed for a light fast hull, AKA, racing hulls

 

[Chinewalker]

IMHO, the OMC 49 cube triple is a far superior motor to the Mercury 3-cylinder of that vintage. I'd choose the 1983 75hp over the 1977 version.

 

[jimmbo]

I concur with Chinewalker about OMCs 49.7 engine being a lot better design than Mercury?s 49.8 engine(loop charging vs. scalloped direct charge, and a carb for each cylinder vs. 2 carbs into 3 cylinder).
3 cylinder engines have a advantage over 2 and 4 cylinder engines when it comes to exhaust tuning. The third cylinder does idle a bit smoother

 

[Keyboardman]

My '76 75 hp idles a lot better than my '74 2cyl 50! The 50 pushed my old heavy Tri Hull at 20 mph. With the 75 on it now, it will do 33.

 

[flyingscott]

The mercury the op is looking at is a 1992 model 60 hp. Probably a better motor than the 1983 75 hp.