I have a 2006 9.9 4-stroke Mercury that I would like to convert to 15 HP. I noticed that the piston bore and stroke are the same, and the block displacement is the same. What about the heads and valves? Are they the same as well?

If so, what parts would I need? Carburator, exhaust manifolds, gaskets....anything else? Do you have part numbers? Is this something I can do myself without much trouble? I am mechanically inclined as my other hobbie is muscle cars.

I'm not sure we don't do horsepower conversions here. Maybe someone else will post some suggestions for you.

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We've seen multiple people attempt this, even changing carbs, etc.

No can do... won't run properly. Save the headache and stay at 9.9.