50 looper vs 85 crossflow

[70's son]

Hi all, trying to decide between a 1974 50 or a 1977 85 crossflow for a1973 starcraft holiday 18 alum. Price to get either on water is same, so a straight power vs weight vs fuel burn shootout. Looking to achieve 25-30 mph cruising speed and 5-6 gph fuel burn. Not sure if there is a performance advantage that justifies the extra weight and fuel burn of the 85. Also its simply more fun to thrash a 50hp at 5gph than tootle about at half throttle with an 85hp just to achieve the same 5gph burn. Im wondering if the speed would be similar at equal fuel burn? Would the top speed of the 85 even be more than 5mph faster than the 50 at wot on an 18ft aluminum? Id rather cruise at 25mph/6gph than 30mph/8.5 gph.Feedback appreciated

 

[70's son]

Also found it interesting to discover that the 1974 evinrude 50 looper is 41.5ci, and the 1974 40hp crossflow is 42.9 ci. The 50hp is a smaller displacement, but gets 1000 more revs, 2 carbs instead of 1, and the more efficient loop system for a whopping 25% power increase. Its wild to think that 50 years ago johnson already understood that there is a replacement for displacement...raise the revs, and dump more fuel in. That was very japanese of them. I love these 70s motors because they were made during a time when omc was interested in being the best. Interesting times and unlimited development budget

 

[jimmbo]

An 18ft boat, even a tinny, is not going to be much fun with a 50hp. The 85hp will certainly be a much more enjoyable drive. Top speed difference with Identical Set Up(Engine Height, Trim Setting, Optimal Propping) will be about 7 mph. Large difference in Acceleration. Throttled back to the top speed of the 50hp, the 85 isn't going to be burning much more fuel.

 

[racerone]

The 2 cylinder 50 appears to be similar in design to a Scott Atwater or Mc Cullough.----In my opinion.

 

[saltchuckmatt]

Boats are best, outboard wise, to be slightly over powered. They don't have to work as hard. Old school 2 strokes are based on the amount of cylinders fuel usage wise. If your an old "granny" you might get that consumption...everyone else, nope.

 

[racerone]

A V-4 gets best fuel economy around 3600 / 4000 RPM.----A 100 HP at 3600 RPM might run as economical as a 50 at full throttle.