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.

 

[tphoyt]

It’s always good to have the extra power if ya need it. If you going to be hauling a lot of gear or friends it may come in handy more than ya think. I’d go for the larger hp myself.

 

[70's son]

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.

Thankyou for the feedback. That sounds logical about fuel economy...I didnt realize it would so much faster though. More than 5mph gain is signifigant. The value of each motor changes with how boat is used i guess. For example I use my boat to travel distance ....so a 50hp travelling at 20 mph at wot for 30miles would use the same fuel as an 85 travelling at 30mph(wot) but take 30min longer. So less time and more speed is better for me However, if i was using my boat for doing circles in front of a cottage then id likely prefer the extra 30min of tubing time id get with the 50 over the extra speed of the 85. But i dont.... so 85 it is! Thanks for the help

 

[jimmbo]

The 85 will be a much better choice for any Watersport.

 

[70's son]

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.

Yes good point. The 50 is my first looper so i was more curious to understand what the equivalent hp on a crossflow would need to be to equal performance. I noticed that the 1974 40hp 2cyl crossflow has almost 2 ci more displacement than the looper 50 of same year, but the looper revs to 6k, while crossflow only revs to 5k, due to heavier pistons. I was wondering how much bigger crossflow motor with 1000 less revs needed to be to equal performance of looper with 1000 more revs. But I was looking at it like a motorcycle....750 4cyl vs 999 2cyl sort of thing. But then it dawned on me, lol, that they dont sell outboard motors by cc's like motorcycles! So a 50 hp crossflow will have the same hp as a 50hp looper but will need more displacement to get there due to lower rev limit. I was looking at it as if crossflow needed more hp to be equal, rather than more displacement. Thanks for the feedback. Im curious to know why you dont believe an 85 can do 25-30mph at 6gph? My understanding is 85hp=8.5gph wot. So i figured 65-75% throttle should be able to do that no problem. Cheers

 

[70's son]

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.

thanks for the reply. Yes that was my line of thinking as well. My 1974 looper 50 is too crazy and new technology for me! I think ill save it as back up and go get the lazy 85...suits my style better anyways. Cheers

 

[jimmbo]

50hp from a Crossflow is the same as 50hp from a Looper. There may be slight differences in Fuel Consumption, and well as how the Engine Runs, Loopers tend to be a little Skittish at idle, while crossflows a bit smoother. Crossflows that can rev higher than the 40hp OMC, are certainly possible, Mercury had its Direct Charge(Crossflow Variant) Motors running close to 6000rpm as production motors, while their Racing Motors were running far higher than that. To raise the Rpm Range, changes to Port Timing, Induction, and Exhaust were done. The 85hp OMC has a WOT range of 4500-5500rpm, which isn't much less than the Looper 50hp
Often, 2 or 3 engines of the same displacement could see a Horsepower Difference of 50%. There were trade-offs, poorer low Rpm Performance/smoothness. Temperamental with regards to tuning.
For decades, Mercury made a 4 cylinder Crossflow 50hp, it was 44 cubic inches, and had a WOT Range of 4800-5300, later years it was 5000-5500. Idled very smoothly, compared to either the 2 cylinder 40hp or 50hp OMCs

 

[70's son]

It’s always good to have the extra power if ya need it. If you going to be hauling a lot of gear or friends it may come in handy more than ya think. I’d go for the larger hp myself.

good advice...

 

[jimmbo]

FWIW, I have never heard a Boater complain that they had Too Much Power, unless he/she put far more than the Max Rated HP on the Boat

 

[70's son]

50hp from a Crossflow is the same as 50hp from a Looper. There may be slight differences in Fuel Consumption, and well as how the Engine Runs, Loopers tend to be a little Skittish at idle, while crossflows a bit smoother. Crossflows that can rev higher than the 40hp OMC, are certainly possible, Mercury had its Direct Charge(Crossflow Variant) Motors running close to 6000rpm as production motors, while their Racing Motors were running far higher than that. To raise the Rpm Range, changes to Port Timing, Induction, and Exhaust were done. Often, 2 or 3 engines of the same displacement could see a Horsepower Difference of 50%. There were trade-offs, poorer low Rpm Performance/smoothness. Temperamental with regards to tuning.
For decades, Mercury made a 4 cylinder Crossflow 50hp, it was 44 cubic inches, and had a WOT Range of 4800-5300, later years it was 5000-5500. Idled very smoothly, compared to either the 2 cylinder 40hp or 50hp OMCs

Very interesting, thankyou. Ive heard as well that 70s merc were often smaller diplacement than johnsons but revved higher toget same hp. I have and still do own several crossflows but this is my first looper. I had heard loopers were better but i think ill stick with crossflows.

 

[jimmbo]

Loopers are considered more advanced(though they have been around for just over 100 yrs), and have some advantages, but are/were more costly to manufacture. As for Mercury smaller but higher revving... OMC for many years used a 92.6 cu in Block for it's 85 HP, with a WOT range of 4500-5500. While Mercury used a 66.6 cu in block for it's 85hp, with a WOT range of 5000-5500. Both were Crossflows, the Merc's was the Crossflow variant, Direct Charge, with Power Porting.

 

[70's son]

FWIW, I have never heard a Boater complain that they had Too Much Power, unless he/she put far more than the Max Rated HP on the Boat

Lol, yes i want the power! But I still dream of finding that happy balance between economy and power... I know it doesnt exist but a 1977 85hp on a 1973 18ft starcraft tinny, for me comes very close. When iwas young i had a 7.5 merc on a 14ft fibreglass. 1 tank of gas would last all weekend but so slow! So i got a 15ft with a65 merc. That was nice and fast but it drained a tank in 30 min! Ive been chasing that balance ever since and i think im finally almost there.

 

[jimmbo]

Myself, that balance would be a nice late 80s merc 135 or 150 V6.

65hp merc running 1/2 hour on 6 gallons is about what my dads 1963 40hp Johnson burned, on a 14ft boat

 

[saltchuckmatt]

I would get a JohnnyRude 70 for that boat. I would search far and wide.