Can a 1970 18hp be converted to a 25hp motor ???

[cajuncook1]

I just had to ask this question! I know another bone head question of someone trying to make a lower power motor into something better. I know the story of the 9.9hp and 15hp Evinrudes. I also know that if you want a 25hp get a 25hp motor.

But......I was looking up parts for my 18hp motor and noticed there are a lot of interchangeable parts for the 18, 20, and 25hp motors. I compared, the power head, exhaust housing, magneto, gear case, reeds, and the carburetors.

The only difference was the complete carburetor assembly, but the core carburetor body on both were the same.

I am not converting my 18hp Evinrude motor, but looking all this up, just got me a little curious. I pulled the information off Evinrude and boats.net website for 18hp and 25hp outboard for year 1970.

Just wondering what the gurus of this excellent forum have to say. I've already put my helmet on.



Evinrude Parts 1970 18002E 1970 POWERHEAD GROUP

0384171 CYLINDER & CRANKCASE ASSEMBLY


Evinrude Parts 1970 25002E 1970 POWERHEAD GROUP

0384171 CYLINDER & CRANKCASE ASSY


Evinrude Parts 1970 18002E 1970 LOWER UNIT GROUP

0383913 EXHAUST HOUSEING ASSY
0313564 EXHAUST TUBE, Inner
0313435 RESTRICTOR, Exhaust housing

Evinrude Parts 1970 25002E 1970 LOWER UNIT GROUP

0383913 EXHAUST HOUSING ASSY
0313564 EXHAUST TUBE, Inner
0313435 RESTRICTOR, Exhaust housing


Evinrude Parts 1970 18002E 1970 GEARCASE GROUP

0383758 GEARCASE ASSY., Less drive shaft & pump [0390977]
0315385 SHAFT, Drive, standard [0321930]


Evinrude Parts 1970 25002E 1970 GEARCASE GROUP

0383758 GEARCASE ASSY., Less drive shaft & pump [0390977]
0315385 SHAFT, Drive, standard [0321930]


Evinrude Parts 1970 18002E 1970 MAGNETO GROUP

0580866 FLYWHEEL & RING GEAR ASSEMBLY
0580858 ARMATURE PLATE ASSEMBLY COMPLETE [0580937]

Evinrude Parts 1970 25002E 1970 MAGNETO GROUP

0580866 FLYWHEEL & RING GEAR ASSEMBLY
0580858 ARMATURE PLATE ASSEMBLY COMPLETE [0580937]

Evinrude Parts 1970 18002E 1970 CARBURETOR GROUP

0279214 LEAF PLATE ASSEMBLY
0383725 CARBURETOR BODY ASSEMBLY
0279290 CARBURETOR ASSEMBLY COMPLETE

Evinrude Parts 1970 25002E 1970 CARBURETOR GROUP

0279214 LEAF PLATE ASSEMBLY
0383725 CARBURETOR BODY ASSEMBLY
0279291 CARBURETOR ASSEMBLY COMPLETE

Thanks,
cajuncook1

 

[JB]

Re: Can a 1970 18hp be converted to a 25hp motor ???

Your 18 can be modified to produce 25 or more HP, but only at high expense and risk. That would not make it a 25, just a hopped up 18, a bomb with a short fuse.

 

[F_R]

Re: Can a 1970 18hp be converted to a 25hp motor ???

The question has been asked and beaten to death many times. Short answer: Look again. The pistons, crankshaft, and cylinder head are different.