# 9.9 Merc converted to 15hp



## limelightsc (Mar 22, 2008)

I just purchased the 15'4 Highsider from flatsteeler. Considering the idea of getting a little more speed out of the 9.9.

For the money, would you go jack plate or convert the motor to a 15? I know it's simple...do both.

I would love to hear the performance comparisons from those of you that have made the mortifications. Tried to search the forum, came up empty.

Glad to own the Gheenoe, by the way. Took here out in a gale and she still ran great. I've been lurking around these parts for some time and it is glad to finally have a reason to!

From Charleston,
GP


----------



## inboardgheenoeguy (Dec 17, 2006)

Contact Capt Ron he has mod. his 9.9 before


----------



## Mikemv (Jan 12, 2007)

As long as we are asking Capt. Ron, can a 2006 Merc F9.9EH be modified to a 15HP or only 2 strokes? Thanks, Mike


----------



## backwaterbandits (Dec 15, 2006)

Yep, CR knows the deal!  Dave


----------



## Guest (Apr 1, 2008)

Lets keep this to the 9.9/15 Merc two stroke since the four stroke does not share the same bore and stroke as does the two stroke. 

That's your answer Mikemv. You 9.9 four stroke does not have the same displacement as the 15 so it's doubtful you will ever develop much over 10 HP.

The 9.9 and 15 2 smokes share the same parts except the 15 has a bigger carb. (not physically but bigger jets etc.) and a tuned exhaust. Purchase these two parts and the proper gaskets, do the swap and you'll have a 15. Be advised you will be exceeding the USCG max HP rating of the craft though. IMHO, a 9.9 2 smoke converted to a 15 is the perfect motor for the NMZ or HSd'r. Pretty sure the cost of the parts will run around $450.00 and about $650.00 installed. I have Advanced Marine in Holiday do my work.

Tom C makes a nice little skinny jack plate that will allow you to tweak your motor height without turning your transom to swiss cheese. If you can't do both then I would shim the motor with the anti ventilation plate some where between even with the bottom of the boat and 1/2" above.

This part is important for you guys running 6, 8, 9.9 and 15 Merc two smokes. The water pickup for these motors is on the underside of the anti ventilation plate. Jacking the motor up allows air to enter the water pump and can cause damage to the impeller and/or the shims. I suggest using a plate attached to the anti ventilation plate to help keep water at the foot. I used a cut down "Bob's" and a homemade one I was experimenting with but I'm sure the other ones like Dole Fin etc. on the market will do the job.

I found that the stock 9 x 9 prop gave pretty decent overall performance but if you want to jack the motor up to it's max you will need to get a 4 blade prop. The lowest pitch Power Tech would make was a 9 x 8 - 4 blade and unless you run a light boat, it still did not develop enough RPM's to suite me. I want my boats capable of maxing the RPMs with a light load. It you are not turning over 5 grand then you might as well be running a 9.9.

as always, just my .00000000000000000000000000000000002 sense
CR


----------



## limelightsc (Mar 22, 2008)

for the money, could you keep the 9.9 as is and get some extra performance out of a jackplate? 

The motor fires every pull and really runs great. Hate to think about messing it up. 

If you had to do one or the other, which one would you do?


----------



## Guest (Apr 3, 2008)

> for the money, could you keep the 9.9 as is and get some extra performance out of a jackplate?
> 
> The motor fires every pull and really runs great. Hate to think about messing it up.
> 
> If you had to do one or the other, which one would you do?



Lets keep this to the 9.9/15 Merc two stroke since the four stroke does not share the same bore and stroke as does the two stroke. 

That's your answer Mikemv. You 9.9 four stroke does not have the same displacement as the 15 so it's doubtful you will ever develop much over 10 HP.

The 9.9 and 15 2 smokes share the same parts except the 15 has a bigger carb. (not physically but bigger jets etc.) and a tuned exhaust. Purchase these two parts and the proper gaskets, do the swap and you'll have a 15. Be advised you will be exceeding the USCG max HP rating of the craft though. IMHO, a 9.9 2 smoke converted to a 15 is the perfect motor for the NMZ or HSd'r. Pretty sure the cost of the parts will run around $450.00 and about $650.00 installed. I have Advanced Marine in Holiday do my work.

Tom C makes a nice little skinny jack plate that will allow you to tweak your motor height without turning your transom to swiss cheese. If you can't do both then I would shim the motor with the anti ventilation plate some where between even with the bottom of the boat and 1/2" above.

This part is important for you guys running 6, 8, 9.9 and 15 Merc two smokes. The water pickup for these motors is on the underside of the anti ventilation plate. Jacking the motor up allows air to enter the water pump and can cause damage to the impeller and/or the shims. I suggest using a plate attached to the anti ventilation plate to help keep water at the foot. I used a cut down "Bob's" and a homemade one I was experimenting with but I'm sure the other ones like Dole Fin etc. on the market will do the job.

I found that the stock 9 x 9 prop gave pretty decent overall performance but if you want to jack the motor up to it's max you will need to get a 4 blade prop. The lowest pitch Power Tech would make was a 9 x 8 - 4 blade and unless you run a light boat, it still did not develop enough RPM's to suite me. I want my boats capable of maxing the RPMs with a light load. It you are not turning over 5 grand then you might as well be running a 9.9.

as always, just my .00000000000000000000000000000000002 sense
CR


----------



## Lil_Tate (Dec 18, 2006)

I have a 5hp 2 smoke merc.  Anyway to increase my HP at all on that good little engine.


----------



## beavis (Dec 11, 2006)

> I have a 5hp 2 smoke merc.  Anyway to increase my HP at all on that good little engine.



one word for u there big guy. 

diet  [smiley=1-sillyface.gif]


couldn't resist that one tater


----------



## Guest (Apr 3, 2008)

> > I have a 5hp 2 smoke merc. Anyway to increase my HP at all on that good little engine.
> 
> 
> 
> ...


RJ, let's be realistic. :

Tate, buy a bigger motor.


----------



## FlatsSteeler (Dec 10, 2006)

Greg I am glad the motor & Gheenoe are working out for you..........That motor is really excellent.....


----------

