Which has more power, 1985 25hp or 1988 20hp?

[headdamage]

I'm looking for a motor for my Mk2 Zodiac. I've found a couple that look to be in good shape, one is a 1985 Johnson (exhaust doesn't go through the hub) and one is a 1988 20hp Evinrude (exhaust through the hub). With the different exhausts and the change in power ratings in the mid 1980's I'm thinking the 1988 20hp might have more real world power than the 1985 25hp. I'm I correct?

Also the I think it would be possible to further up the power on the 1988 by using a 35hp carb and intake.

I've had a Evinrude 1975 15hp with the through hub exhaust for years and love it. I've also had a long shaft Evinrude 25hp 1988 before so I'm inclined to go with the 1988 just because it appears to be a more familiar engine to me.

 

[HighTrim]

Re: Which has more power, 1985 25hp or 1988 20hp?

1986 was the official change in hp rating from the crank to the prop.

That being said, you only get about a 10-12 percent loss through the gearcase, that representing roughly 2.5hp for the 25hp for easy math. You would hardly notice the difference I would think unless you are spiderman.

You may notice a torque difference depending on whether the motors were looper or crossflow scavenged, but without knowing for sure I would be guessing. If the 88 is a looper and the 85 a crossflow, then I would say the torque difference would be noticable. Wouldnt know without looking at them though.

 

[headdamage]

Re: Which has more power, 1985 25hp or 1988 20hp?

Photos of the two motors if that helps:

 

[ChillyB]

Re: Which has more power, 1985 25hp or 1988 20hp?

Does the 25 hp have a motor lift latch? Looks a lot like my 1981 25hp, which does NOT have a lift latch. If the 20hp has a latch and the 25 does not, I'd take the 20 with a latch. And I THINK you could upgrade the carb on the 20 to make it a 25. The later 20 has a stronger lower unit. Note the 25 has the split gearcase around the horizontal prop shaft. I'm not sure it matters, though. Unless there are issues with the split case then it wouldn't matter, and so far as I have learned there are no issues with the split case.

Really, I'd be more interested in the compression numbers than the age and hp rating.

 

[boobie]

Re: Which has more power, 1985 25hp or 1988 20hp?

If it all checks out, I'd go with the '88 20 hp.

 

[jbjennings]

Re: Which has more power, 1985 25hp or 1988 20hp?

The '88 20hp is the better motor, and appears to be in better condition. I'd agree with BOobie and get it.
However, the ignition parts will be more expensive on the '88. I'd almost bet one could get more than 20hp out of the '88 with a carb change, but probably be costly. You might be able to just take the carb off and see if the intake manifold has the same size hole as the carb throat. If not, dremel out the intake manifold to match the carb throat and get your 5hp back-----maybe.
Good luck,
JBJ

 

[headdamage]

Re: Which has more power, 1985 25hp or 1988 20hp?

I'm going to have a look at the 20hp and see it test run, if it seems ok I think I'll take it. The owner is asking $975 which around here is good, I can't find a 35hp for under $2000 and I just can't find a 25hp with the through hub exhaust.

Correction... I got lucky and found a good short shaft 1992 30hp Johnson