info on evinrude 18 hp vs johnson 20 hp?

[dkonrai]

what is the difference between the two? i have a 72 johnson 20 hp, and just acquired a 68 evi 18 hp. they seem almost like the exact motor, so why is one a 18 and the other a 20 hp? lower units seem to be the same as well.

what problems, or what issues should i keep a eye out for on this 68 evi? i originally bought the motor as a spare parts motor, paid 100 for it. it has electric start, short shaft. after looking at this, i think i am going to get this thing running. really clean for how old she is.

thanks
dino

 

[ultra353]

Re: info on evinrude 18 hp vs johnson 20 hp?

Some have said it was just marketing. Pretty much the same motor, same lower units.

 

[dkonrai]

Re: info on evinrude 18 hp vs johnson 20 hp?

Some have said it was just marketing. Pretty much the same motor, same lower units.

?? so the johnson had more ponies x 2?

i guess i have another project another one to revive. compression is all over the place. rings seem a little rusted from sitting. first reading was 60/70. next pull showed 90/80. letting her soak abit in some marvel oil.
thanks again
dino

 

[F_R]

Re: info on evinrude 18 hp vs johnson 20 hp?

I think you will find the 20 has a different cylinder head for higher compression ratio, making those two ponies.

The '68, in equal condition, will slow idle better than the '72 because in '68 they were still dumping the crankcase drains into the lake. '72 was cleaned up a bit by dumping the drains into the upper cylinder for burning. That makes the upper cylinder run too rich, which equals poor idle. Y'all be the judge as to whether or not the lake can tell the difference.

PS, the 1970's were also the years where we were ripping the "smog controls" off our car engines in an attempt to get them to run better. Remember those days?

 

[bonz_d]

Re: info on evinrude 18 hp vs johnson 20 hp?

?? so the johnson had more ponies x 2?

i guess i have another project another one to revive. compression is all over the place. rings seem a little rusted from sitting. first reading was 60/70. next pull showed 90/80. letting her soak abit in some marvel oil.
thanks again
dino

That 90psi compression is the same as I was achieving on my 1964 18hp Rude and it ran very strong and started easily with the pull start so I'd say compression is good to go.

 

[Chinewalker]

Re: info on evinrude 18 hp vs johnson 20 hp?

The 18 and 20 were virtually identical, mechanically speaking. The extra 2hp was well within the fudge factor when rating horsepower. I've run both 18s and 20s over the years and have never noticed any seat-of-the-pants performance difference between the two...

I've heard it said the only difference was the reed stops were opened up a bit on the 20, but I've never confirmed that myself.

The 22-cube 25 got the different cylinder head, piston, crank, etc.

 

[jasper60103]

Re: info on evinrude 18 hp vs johnson 20 hp?

I like the convenience of electric start. I would give it to the best runner.

 

[kfa4303]

Re: info on evinrude 18 hp vs johnson 20 hp?

This may help.

Maintaining Johnson E & FD Serie

I run a '66 20hp Johnson myself and love it, but I doubt it's noticeably faster than it's 18hp cousin. I get about 20 mph +/- on my 14' semi V-hull tinny. Here's a link of my toodling around a local beach.

Wakulla Beach, FL movie.wmv - YouTube

Thankfully, virtually all of the parts between the 2 brands and models are identical and interchangeable.

 

[Sea Rider]

Re: info on evinrude 18 hp vs johnson 20 hp?

Are pistons interchangeable too ? If not 20 has slight bigger pistons than the 18. Same as Tohatsu 15-18 both are alike and parts interchangeable, except pistons, slightly bigger providing 3 HP difference.

Happy Boating

 

[kfa4303]

Re: info on evinrude 18 hp vs johnson 20 hp?

I believe they do share the same pistons (OMC part # 378278). I think the only difference between the 18 and 20 are the reeds and perhaps a carb jet.

 

[dkonrai]

Re: info on evinrude 18 hp vs johnson 20 hp?

tinkering the carb is smaller than the 20. i need to pull off the 18's carb but its in between a 15hp and the 30 hp carb. i got her running (actually ran pretty good considering) and got her warmed up. and now the compression is.........


120/120. sweet ok so now the parts motor is a project motor. darn it, i wanted to rob the starter,lol.

dino