1957 18horse Faster?

[55Crestliner]

Is there anything that can be done to give my motor more power?<br />It's a 1957 Johnson 18 horse. I know the usual answer is to get a bigger motor, but it's on a pretty small boat (12 feet) and I don't want too much weight. I also will not put anything newer than a '59 on my boat, and I don't really have the opportunity to just easily go find a nice 30hp '55 Johnson.<br /><br />The topic below mentions that there was a later model 25 that was created from the 18 horse like mine - can I do the same as the factory did and increase my existing 18?<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=17;t=038450 <br /><br />What would happen if I did increase hp? Would I simply need a bigger prop to keep the rpms where they are now? (about 4600 wot) Would the internals take it?<br /><br />Just to be clear, the motor has the correct size prop for the year, and is at the correct RPM, and runs perfect - I don't need to "tune up" my motor, I want it faster.

 

[Solittle]

Re: 1957 18horse Faster?

That is one neat little rig! Despite Tim Allens cry for MORE POWER - there are time when we should be thankful for what we have got. I woulds leave well enough alone. Just think - - you mentioned that your rig gets 2 adults + 2 kids on plane with a 48 year old 18 hp motor. Paul may jumpin with some tips though - Good luck.

 

[Paul Moir]

Re: 1957 18horse Faster?

I don't have any good info here, but here's a few interesting links if you havn't seen them yet:<br /> Iboats Thread<br /> Another Thread<br /><br />EDIT: Looks like I'm getting too predictable...

 

[steelespike]

Re: 1957 18horse Faster?

I think you are setting some tough paramiters.<br /> If you can find someone with the info you might be able to get to 20 Hp.But 25 is not likely.<br />These things need to be done carefully or you could end up with a "Frankenstein" motor.If your just looking for speed you might try fine tuning the trim.Raise the motor virtically 1/4 inch at a time until just before ventilation becomes a problem If you go with an after market prop with some cup you should be able to go higher.If you can gain an inch you could add close to 3 mph and the prop could add more.When you add cupping you may need to drop down a little in pitch.<br />You might ask Scott at Chinewalkersplace.com He races and has been messing with motors for years.Also has a very interesting site.I think when you eliminate a 30 to 40 hp you are missing some serious speed.Especially if fine tuned as I described.Im pretty sure Scott could give you some tips for safely hot rodding these as well.<br />Id be interested to see how you make out.

 

[reka12]

Re: 1957 18horse Faster?

I understand that my '70 rude 25 is based on the same block as the 18. (Right Paul?). That said, the motor weighs 85 lbs or so and as Paul predicted, I am having a hard time finding a more current motor that would be in the same weight class. I just don't know about '59 models. Mike

 

[cobra 3.0]

Re: 1957 18horse Faster?

Nice rig!<br /><br />My 1997 15 Evinrude 2 stroke flies on a 14 ft aluminum with two people and it weighs somewhere around 74 lbs....you know what they say about an old horse?

 

[Booner]

Re: 1957 18horse Faster?

55Crestliner I have a 57 Johnson 18 hp on a 1962 14'Seaking (duck boat) I would leave well enough alone. I flipped a 12footer a few years ago. I had too much motor on that boat and it got squirrelly when on plane I turned to hard to the left and the back caught water and over I went. I’m lucky I didn't drown it was around 1am on a 120 acre lake. Had to swim with pushing the boat upside down 100 yards or so. Good luck!

 

[Chinewalker]

Re: 1957 18horse Faster?

55C,<br /> Your 18hp is similar to the later 25hp (based on the same 22-cube block), but there are enough differences that could make it hard to convert it. Something you might want to try - the only difference I am aware of between a 1966 Evinrude 18hp and a 1966 Johnson 20hp is the reed stops have been opened up a hair on the 20. I wouldn't try opening up the ones in your motor, rather I'd find a reed plate off a 20hp and install it, keeping in mind that you might have to modify it to accomodate the pressure system. If you install the 20hp reed and stops on your 18hp plate, be sure to LocTite the screws in the centers. I don't know if you'll notice any difference, but it might be worth a try.<br /> The late 1960s 18s, 20s, and 25s also used a larger carburetor, but installing on one your motor would require much jury-rigging to accomodate the linkages, knobs and swapping the intake manifold. That, and the 25hp model used different pistons and cylinder head, too.<br /> It's also not an easy task to just drop a 25hp powerhead under your cowling, as it would have none of the cowling mounts attached and you can's swap the cylinder heads back due to the 25hp having a thermostat and your '57 being a straight cooler...<br /> Having run an 18hp on my own 12-footer, I know that it's certainly a ride with one person aboard. Hate to say it, but if you really need more oomph, you need to go to a bigger motor, which on a 12-footer might not be a good idea.<br />- Scott

 

[WillyBWright]

Re: 1957 18horse Faster?

What is that TWELVE FOOT boat rated for? I doubt it's even rated for what you have on it. I'm staying WAY clear of this one, gentlemen.

 

[steelespike]

Re: 1957 18horse Faster?

As I recall the older Crestliners had a fairly high HP rating.If I remember right my 56 14 ft utility was rated for 35 hp.

 

[Ronald1]

Re: 1957 18horse Faster?

Wow, what a neet little boat! I'm currently working on an old 12' v-bottom with a 1955 Johnson 5.5. You have inspired me to scrap the 5.5 and hang my 35 Evinrude on the back! LOL! CT

 

[55Crestliner]

Re: 1957 18horse Faster?

The boat is rated for either a 30 or a 35, the second digit has a scratch going through it. (This is why I'm not certain what year my boat is, they went to 35 for the same model in '57 IIRC)<br />You know how people say (some of you I bet) that a boat should have no less than a certain(80? Can't recal the exact number)percent of the boats max capacity? Well that would put it conservatively at 25hp. Anyway, that's another forums topic.<br /><br />I'm certainly not interested in a Frankenstein motor, at least not with this one anyway. I just wasn't sure if it was something simple, like a 5 minute bolt on or something. If I had the 25 that was based on mine, I would not have asked to make it a 30, you know what I mean? It wasn't really a blanket "how do I hotrod my motor", it was specifically asked about my motor and how it evolved into those later ones. Sounds like more than I thought, Sounds like I'll leave it alone.<br />All good info, even the flipping over story, it's all taken seriously.<br /><br />btw, the motor height was addressed, (thanks for the sug.)in fact it's a little too high right now, I need to drop it a little.

 

[steelespike]

Re: 1957 18horse Faster?

You might be able to keep the height where it is if you play with the prop and maybe get just a "smidge" more speed.