evenrude more power

[nightcrew]

Is it possible to get more horsepower out of my 1989 8 h.p. evenrude and how.

[litscot]

Yes the proper way to gain horsepower is to remove this engine from your inventory and when this step is complete purchase a more powerful engine.

Just kidding,I'm sorry but I don't know enough to help but I will keep an eye on this thread because I am also interested.

[kenJ]

I think the only way to increase the HP would be to either increase the size of the piston called boring in the engine business or increasing the compression. In either case you would need to take the engine to a machine shop. Is there enough casing to increase the bore to that of a 10hp? Can the cylinder head be milled to increase the compression? Those are questions maybe they can answer. Another question to ask, is the engine designed strong enough to accept the changes you want to make. Last thing you want to have is a bomb sitting next to you.

[marshmat]

There aren't many mods available for an engine this small. Internal machining as KenJ suggests is the only way to realize significant gains, and that will probably prove more expensive than replacing it with a 9.9 or 15.
What type of boat is the motor used on?
Start by cleaning it up though- check the carb, it might need a rebuild, get it properly jetted for your conditions. Get the carbon buildups out of the cylinders. This will help a bit.

[Frosty]

Check to see if your 8hp is the same block as the 10 or what ever the next sizes are,-- If it is then find out how. Then change whats different. Some small engines are like this 2.5 and 3hp are the same exept for carb restrictions and timing. Easy mod, about 30 minutes.
If this is not the case then it is really not worth the money trying to increase power by tuning or boring.

[marshmat]

If I recall correctly, the '89 Evinrude 8 is the highest rated version of that block.... the 9.9, the next one up, shares its block with the 15.

[desertgoldhound]

I dont know that much about boat moters but couldn't you port your valves. This would probaly give you a little gain. It would help with gas if it can be done. You can do this yourself however make sure it is clean afterwords you don't wont any shavings left behind. I know this works realy well on auto moters I don't know why it wouldn't work on boat moters but then again I will be doing my first one here soon and never opened one of them up to see what is inside.

[Frosty]

Boy are you in for a shock

[marshmat]

goldhound- the 1989 Evinrude 8 was a two stroke; it doesn't have valves- rather, it has holes in the cylinder wall that are covered and opened by the piston itself. It's possible on bigger motors for a very skilled craftsman to smooth the shape of these ports a bit, for a slight power gain, but on an 8hp it will do next to nothing and cost more than the motor's worth.

[desertgoldhound]

So its not as easy as it is for a car or truck moter. And It doesn't give much of an increase. I learned something new. I have never done work on any thing other then car moters sorry.

I guess my sugestion was more of a learning curve for me then the poster sorry

[marshmat]

As to the original question, can we get more out of an '89 Rude 8: Cleaning it up back to factory spec, getting all the gunk out, possibly tweaking the carbs might net you 0.5 hp. Maybe 1 hp if it's really gummed up right now. To get 10 hp out of your 8, would probably take over a thousand bucks of internal machining and new parts. A used 9.9 would be a cheaper and more reliable option.