9.9 hp upgraded to an 18hp...possible?

[Mike Ku]

I live in an area where the biggest outboard I can put in the water is a 9.9hp. I was told that you can buy a 9.9hp and replace the carburator on it with a carb form an 18hp and there by change it to an 18hp motor. This would make me a happy camper as then when I use the boat in another state I still have a strong set up. My boat currently has an old 18 hp motor which is getting tired and I take risks using it in my area. Any suggestions or tips? Thanks!

 

[kev_79]

Re: 9.9 hp upgraded to an 18hp...possible?

I have heard that you can make a 9.9 a 15. The fact is that most 9.9's have the same block as a 15 hp, they are just detuned to meet hp regulations. If the 9.9 and 18 are the same type of engine, then I would check with a dealer to see if the displacement, exhaust restrictions are the same. If so, then the carb swap would probably work. Good luck, and tell us how it goes.

 

[JB]

Re: 9.9 hp upgraded to an 18hp...possible?

A carb swap will not turn a 9.9 into an 18, or a 15. There are other differences. If you are determined to break your local law, the most efficient way to do it is to get a 15 and put a 9.9 bonnet or 9.9 decals on it.<br /><br />Good luck.<br />JB

 

[kev_79]

Re: 9.9 hp upgraded to an 18hp...possible?

JB,<br /> I was wondering what those other differences were. I own a 115 merc, and it is identical to the 100, and 125 models, except for carburators and exhaust plates. It makes sense that the 9.9 and 15's should be basically the same, except carb, or exhaust plate, right. I want to know, because my good friend has a 9.9 evinrude, and a 15 of the same year, but the 15 has fell to detonation. He said they look the same with the cover's off, but I haven't seen them yet. I told him we could probably do it, but I dont' want him to haul them here from his parent's house if we can't.

 

[JB]

Re: 9.9 hp upgraded to an 18hp...possible?

To know all of the differences, Kev, you need both parts lists. Change everything that has a different part #, (probably includes the block and gears in the foot), then tune according to the 15 manual.<br /><br />You will end up with an engine that has about 20% more torque, but turns higher rpm to achieve its 150% hp numbers.<br /><br />As I have said before, outboard "horsepower" is a marketing toy. Anyone who has compared holeshot between a 115 Cubic inch V4 "90" and a 80-some cubic inch inline 3 "90" with the same gear ratio and prop will understand what I mean.<br /><br />If you really want more usable power, get more cubic inches.<br /><br />Red sky at night. . .<br />JB