Posts: 3480
Location: Elk River, Minnesota | Hiya,
I would say go for the highest HP you can get and stay with the remote steer. One major advantage I think you will see is that somewhere in the late 80s? I believe they changed the HP ratings on the motors to be at the prop rather than at the main shaft of the engine.
If my memory serves me correctly, the current mariner on there would be acting more like a 35 to 40hp motor at the prop, whereas on a newer generation motor that is 50hp, it would be 50 hp at the prop... A nice gain...
So...if you go with a 70 or 75, you'd have a boat that would move along nicely.
the only thing I would be concerned with is going to a 4 stroke motor, though...with that vintage of boat, they were never designed for the weight of a 4 stroke as compared to the 2 stroke. It is not in that the transom couldn't handle it...but level floatation. I could easily see if a 4 stoke was put on, the boat would squat quite a bit.
I'd say, if you can find it, go with a 70hp Yamaha. It is the same displacement as their 90hp model, but with a little more in it than 70 hp. Also if memory serves me correctly, motor manufacturers are able to list a motor's HP at a certain value so long as it is within 10% of what it dyno'd at. So...when you see motors that have the same displacement but different HP, they are playing with fuel/air settings with carbs motor, and possibly exhaust tuners as well and different head tightness/compression...at least that was the case with yamaha.
So...the yamaha 70hp most likely was running more around the lines of 76hp, while the 90 hp was most likely running like an 82hp or so....close enough to call them 70 and 90 with jetting, exhaust tuning and head compression...
Steve
Edited by VMS 3/7/2018 8:18 PM
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