1975 Johnson 50 hp upgrade to higher horsepower

[Billansor]

Hello<br />1975 Johnson 50 HP Model 50ESL75B<br /><br />I saw in one of the posts that a 9.9 hp was upgrade to a 15 hp. Which surprised me and made me wonder if such a thing is done on this motor or is it just not much of a motor to try to do this to?? or am I just being naive and stupid in this thing???<br /><br />Thanks for answering questions that I do not know. The only question that is stupid is one that you do not ask..<br /><br />Bill

 

[WillyBWright]

Re: 1975 Johnson 50 hp upgrade to higher horsepower

You don't want to squeeze more power out of that motor. It's wound pretty tight already. They made a 60Hp twin for a few years, but they had a tendency to melt-down. Upgrading is expensive and is assured to shorten the life expectancy of the motor. That goes for the 9.9/15 "upgrades" too. There are many factors involved. Not just carbs.

 

[Billansor]

Re: 1975 Johnson 50 hp upgrade to higher horsepower

Okay, that answered a question that I did not know that you woiuld shorten the life of the motor by doing that. it makes sense. Does a two cylinder have more rpms than say a three or four cylinder of the same horsepower and thereby having more speed??<br />Thank you for answering..<br />Bill

 

[WillyBWright]

Re: 1975 Johnson 50 hp upgrade to higher horsepower

The RPMs stay about the same. Most run wide open at around 5500. Number of cylinders doesn't matter. More pistons for the same horsepower usually means they get smaller as you increase the number of pistons. But other things can affect horsepower too. Like exhaust tuning, carb throat size, number and size of reeds, and others. Mercury made a 50 4-cylinder for a bunch of years. The Johnson was a bit quicker out of the hole and the Merc was slightly faster, but the differences weren't great.<br /><br />Not that it means much, but the 50 twins are about the noisiest outboard on muffs. They have quite a bark.

 

[Dhadley]

Re: 1975 Johnson 50 hp upgrade to higher horsepower

It is possible, with your motor, to make it the same as the 60 hp 2 cylinder rather easily. We've done it several times. We have yet to have an owner pleased. The majority of the time the set up was off on the 40 or 50 so changing some things didnt really make any difference, therefore the disappointment.<br /><br />You still have the same bore, stroke and gear ratio. Any increase in torque is minimal. Most recreational hulls do not respond to such small increases in torque. <br /><br />The same goes for just about any family of motors you can think of (9.9/15, 40/50/60, 115/140, 120/140, 150/175, 200/225). Without increasing torque significantly you have to work with set up to increase efficiency and reduce slip.<br /><br />Take for example a crossflow and a looper. There are equal hp models in each design but the looper, because of torque, is stronger. <br /><br />All this long-windness takes us back to one thing. Tell us more about your set up and how it performs. Perhaps there is something to be gained without spending a lot of money.<br /><br />Good luck!

 

[ledgefinder]

Re: 1975 Johnson 50 hp upgrade to higher horsepower

Those 50hp twins really like to rev - make sure you're propped to turn 6000+ before you worry about modifying it to 60hp. They are pretty highly tuned (one of OMCs first loopers), and are particularly soft in the midsection of the powerband. Great motor for something fairly light, like an old 15' aluminum hull. <br /><br />Prop it for 6000+, and get it as high as you can on the transom - go higher until you start to cavitate on turns/takeoff, or lose water pressure. <br /><br />Note that the transom length on those OMCs is more like 21" rather than the exactly 20" on Mercs, so really you should be minimum of an inch off a standard 20" transom - probably more. As a real rough rule of thumb, I drill the holes with the motor hanging right on the transom, then jack the motor up to the next to last set of holes (next to last highest). This'll sometimes be too high for skiing, depending on your hull and other factors. Just a rough rule of thumb, you have to experiment to find the right place.

 

[Billansor]

Re: 1975 Johnson 50 hp upgrade to higher horsepower

Hi and WOW<br />Thanks for all the replies. <br />The boat is a 1969 Larson fifteen footer. Its fiberglass and is a clunker. Previous posts have been made in reference to a bad spark hence we have replaced the coils but have not gone back out to see what the results were. In fact before we do that we will check and see if the spark that was so poor before is now better. At that point we will know more about performance.<br /><br />To the other reply in the area of 6000 rpm. How does one know the rpm. Obviously I am a newbie, a green horn, a raw un in not knowing all of this but am learning with each reply that you folks have given.<br />Many thanks<br />Bill

 

[v12mac]

Re: 1975 Johnson 50 hp upgrade to higher horsepower

Ya need a tach, do an Iboats serch lots of options.<br />Mac

 

[jiipee62]

Re: 1975 Johnson 50 hp upgrade to higher horsepower

I have -97 2 cyl 50hp, and seems that I may get -85 60hp poverhead for nearly nothing. Is there any difference in ignition, exhaust etc. between those two, meaning can I get 60 hp with changing only carbs and something or do I need more parts than the poverhead?

Thanks,
Jyrki
Finland
Europe

 

[Shinyboat]

Hello<br />1975 Johnson 50 HP Model 50ESL75B<br /><br />I saw in one of the posts that a 9.9 hp was upgrade to a 15 hp. Which surprised me and made me wonder if such a thing is done on this motor or is it just not much of a motor to try to do this to?? or am I just being naive and stupid in this thing???<br /><br />Thanks for answering questions that I do not know. The only question that is stupid is one that you do not ask..<br /><br />Bill

Did you end up doing anything? I am contemplating the same thing on a 91 Johnson 50.

 

[jbcurt00]

Did you end up doing anything? I am contemplating the same thing on a 91 Johnson 50.

It's been 18yrs since Bill was on iboats and after posting this, never came back..... not likely to get or reply to your message
.closed