Changing a 9.9hp Yamaha to a 15hp

[fisherman7]

I have a 2007 2 stroke 9.9hp and the dealer told me I could change the carb and make it into a 15hp.

 

I was wondering if anyone has done this or has any advice?

 

Thanks!

[GeorgeJ]

more fuel + more air = more power. I was surprised to find out that some smaller outboards share the same bore and stroke but the higher horse power rating comes with carb and air intake changes and maybe a bit of a timing change.

[irishfield]

It's not just the small ones... all the 6 cylinder Verado's 200/225/250/275/300 are the same bore/stroke with HP being controlled by the computer and probably injector port sizes.

 

Just be sure to leave the 9.9 cowling on so you don't have to register the boat...

[ecmilley]

while the 9.9 and the 15 yams share the same block and corresponding bore and stroke, when you factor in the price of the carb, intake runners exhaust system and possibly a flywheel to alter ignition timing is is cheaper to sell the 9.9 and buy the 15 hp engine

[Bernie]

more fuel + more air = more power. I was surprised to find out that some smaller outboards share the same bore and stroke but the higher horse power rating comes with carb and air intake changes and maybe a bit of a timing change.

 

George it may seem that way but there is usually a little more to it than that. Just because you add the capability of more flow at the intake doesn't mean the engine is capable of pulling it. Porting often comes into play here as well as exhaust. It may have the same bore and stroke but the ports might be smaller.

Edited March 31, 2009 by Bernie

[GeorgeJ]

George it may seem that way but there is usually a little more to it than that. Just because you add the capability of more flow at the intake doesn't mean the engine is capable of pulling it. Porting often comes into play here as well as exhaust. It may have the same bore and stroke but the ports might be smaller.

 

I see, I'm not surprised that there are are changes necessary to get the hp rating up. I tend to agree with what someone else said, sell the 9.9 and buy the 15hp.

[Bernie]

I see, I'm not surprised that there are are changes necessary to get the hp rating up. I tend to agree with what someone else said, sell the 9.9 and buy the 15hp.

 

Don't get me wrong here George, it isn't always the case. The OMC 9.9 to 15 conversion is as simple as having a proper drill bit size (and knowing which hole)

[fisherman7]

Thanks for the replies. According to the mechanic, all that needs to be done is changing the reeds in the carb. I'm having it done this Sat and will probably test it out later in May. I'll let you know how it zips my little inflatable along.

[ld17]

I had a 15hp on my inflatable and got around 23mph out of it.

[boatman]

Thanks for the replies. According to the mechanic, all that needs to be done is changing the reeds in the carb. I'm having it done this Sat and will probably test it out later in May. I'll let you know how it zips my little inflatable along.

 

I'm interested to hear how it turns out. Sometimes its an easy mod and others times its not. Its always year and model dependent.

 

I look forward to reading about your results. Any chance you will have any GPS results before and after the mod?