20 hp hop up

[racefan2]

Hello,<br /> It is my first post here so please be gentle. I live in a motor limited state so the local hp rating is only 20 so the big rage is to get the 20 hp motors and hop them up. My question is as follows.<br />I have just purchased a 1991 Evinrude 20 Hp motor and have been told by a few different people that you can bolt a 30 or 35 hp OMC carb on the motor I have and it will become that size motor. I have talked to a few OMC dealers and was told no way there are to many differences in timing and other things which I sorta don't beleive but don't want to purchase a 30 hp carb for nothing. Could somebody answer this question for me?<br /><br />Also the fin on the bottom of the motor right behind the prob mounted on the cavitation plate is adjustable but why would you want to turn =change the direction? Is that to compensate for a bit of the tork pull a bit?

 

[Johnnielund]

Re: 20 hp hop up

Racefan; I have a 1990 25 hp Johnson that the previous owner had converted to a 30 hp by a very reputable marina here in northern Illinois. I have a 16’ Lund Explorer and am very happy with this boat/motor combination. According to Joe Reeves the 25 and 30 have the same block, cyl head, crankshaft, rods, pistons, leaf plate, leaf valves etc. The differences between the two are as follows:<br /><br />The throat hole venturi on the on the carb and manifold is larger on the 30 than the 25.<br /><br />30hp is hit at 5500 rpm. 25hp is hit at 5000 rpm.<br /><br />The cam, which is attached to the magneto armature plate, is different. The 30hp cam is # 326876. The 25hp cam is # 334750.<br /><br />The orifice at the extreme top of the carburetor is different. The 30hp is # 39 (.039) # 334568. The 25hp is # 30 (.030) # 317473.<br /><br />The high speed jet, located at the center bottom portion of the float chamber is different. The 30hp is #65D (.065) #327541. The 25hp is #51 (.051) #331567.<br /><br />I don't know how much difference there is between the 20 HP and the 25 HP and between 1990 and 1991. Best bet would be to get a parts book for each and try to match part numbers. I do know that later model years had different exhaust port timming between the 25 and 30 HP.<br /><br />I hope this information is helpful to you. It is my understanding that trying to increase hp is usually not a good idea, however I think in the case of this particular motor it works well.

 

[Silvertip]

Re: 20 hp hop up

Just curious, but on your HP limited lakes, don't the "enforcers" have a clue that some 20 HP engines just seem to be a lot faster than others?

 

[racefan2]

Re: 20 hp hop up

Yes but thay cannot do nothing as long as the model and serial is a factory 20 hp motor. It will cost them way to much to get a dyno brought it just to test 1 motor to prove it is bigger but it still is legally a 20 hp motor just like building your car motor I guess.

 

[racefan2]

Re: 20 hp hop up

Johnnielund <br />Thank you for the reply. I may just look for a 25hp carb and live with that. Right now I am about 26mph on the river going against the current with full load with the 20 hp rude. I have a 16 ft semi V bass full decked consol duel battery and it is a wide boat about 82 inch beam in the center so I beleive that is good with a 20. Now I do have a CMC Tilt and Trim PT30 and it works like a jacking plate also lifting the motor about 3 or more inches and moving it back 5 inches. I figure the total weight is about 1100 lbs full load

 

[mrloring]

Re: 20 hp hop up

racefan2<br /><br />Have you ever been stopped and had them check your model #/Serial #? <br /> <br />Just curious as I camp every year at Pymatuning(still 9.9hp) and a dealer up there told me the most common engine he sells is a 20hp, and that the owners put 9.9 stickers on it. I have heard of doing this with 15hp because they are the same block etc. He said with the increased size of the 4-strokes you can get away with it. <br />

 

[Silvertip]

Re: 20 hp hop up

A dyno isn't needed to tell whether an engine is legal or not. One need only check (in your case) intake manifold and carb part numbers. Just those two items means the engine is modified from stock and therefore not legal. But then it all depends on how the rules for the lake are written. Another example of local officials creating a law that doesn't get enforced.

 

[mrloring]

Re: 20 hp hop up

Seems that would be kinda difficult to enforce. Look on ebay at how many outboards say "stickers say it is xxhp, but it is really xxhp."

 

[racefan2]

Re: 20 hp hop up

mrloring <br />No I have never been stopped. I fish Pymatuning a good bit and just removed my 9.9 Johnson with a 15 carb and it has been used that way since 1989. I have been stopped looking at life jackets and a throwable on a holiday.<br />The deal you speak of must be the Honda dealer right at Pymatuning and has the same name I beleive ( They do all my motor work ) told me the same thing trying to get me to buy a Honda 4 stroke 20. The warden seems to be happy as long as the decals say 9.9 but this cannot be on a boat that is running 35 mph with a 9.9 LOL. Most of the boats that fish the bass tournament on Lake Aurther are 30 HP motors full out with 30hp serial numbers and model numbers with a reddecaled hood. Two guys are running at 38 mph I have heard. I do not know how they get away with that.

 

[racefan2]

Re: 20 hp hop up

Upinsmoke<br /> It says 20 HP limit on the signs at the launch that is it. Also motor boats only no personal motorcrafs like jet skis if they make a small 20 hp one.

 

[mrloring]

Re: 20 hp hop up

I was thinking about going to Prince Gallitzin next year. I have a 1989 28hp Johnson that I was gonna do up a new 20 hood for.

 

[mrloring]

Re: 20 hp hop up

As for the dealer it was across the bridge from Epsyville. I heard the reason that Pymatuning isn't yet 20hp is the top dawg in Ohio is a sailboat man.

 

[racefan2]

Re: 20 hp hop up

Yes you are exactly right about the ohio side. I say toss him out of office and open the lake up with no wake zones in shallow areas.

 

[rodbolt]

Re: 20 hp hop up

the intake manifold on the 20 is way smaller than the 25-35, I cant remember about the port timing and gear ratio. its all something to look at. the last one I did I used the midsection from an 87 or so 20 with the powerhead and gearcase off a 35