Diff between motors

[bare3176]

Can anyone tell me what the differences are between the 20hp and 25hp engines around 72. I have a 20r72r and would like to get a little more power out of my motor. I have a manual that list these motors together with all the parts being the same. Whats the difference?

 

[Willyclay]

Re: Diff between motors

Welcome to the iboats.com forum. The experts here can help you with any issues involving a boat, motor and trailer. The link below is to a thread about the same subject. FYI, when I see posts by F R, Tashasdaddy and Chinewalker, I pay attention. Good luck!

http://forums.iboats.com/showthread.php?t=360057

 

[Dhadley]

Re: Diff between motors

The 18 E-rude and the 20 Johnson are the same. The 25 uses the same block and a "balanced" crankshaft. The 25 has a different head. The 18 / 20 piston has a different wrist pin height. The 18 / 20 crank will safely run 6000 or so. You could put a 25 head on your 20 but you'll have to run 93 octane and you may still burn a piston. Be real careful about timing.

When we used to build a 25 SS based on an OMC block we used either block, a 25 crank was prefered but not a deal breaker, the 18 / 20 pistons and the 25 head. But we ran those on small hydros which would respond to small torque increases. But we used Champion Hot Rod gearcases too.

On most recreational boats you'd be way ahead to play with set up and props.

 

[bare3176]

Re: Diff between motors

Thanks guys just wondering. Somebody told me it had to do with the openings in the cylinder walls would be higher or lower, he was talking about alot larger engine than mine.

 

[Dhadley]

Re: Diff between motors

On some motors in the same family port area and port timing does have a lot to do with it. On the specific model you asked about the blocks happen to be the same.