9.9hp outboard "upgraded" to 15hp?

[MarkSF]

Worth noting that the 6hp 2 stroke Yamaha is easily upgradeable to 8, with a carb and exhaust manifold.

[donradcliffe]

Originally Posted by Caravela1986

I had my Tohatsu 9.9 HP 2 stroke upgraded in Panama City Panama local Tohatsu dealer
and have been very satisfied.

It is For Sale in NJ for US $$ 500 Send me personal message if interested

I did my own upgrade to that engine. Turns out the biggest difference was that the throttle cam on the 9.9 only open the throttle half way

[senormechanico]

Originally Posted by donradcliffe

I did my own upgrade to that engine. Turns out the biggest difference was that the throttle cam on the 9.9 only open the throttle half way

Exactly right. I did the same conversion to our Tohatsu 9.9 in 1993.
Added a S.S. prop and it was a killer combination on our Avon 3.10 RIB.
While in Mexico, we could put it on plane with four people and a pile of groceries and get out thru the surf back to the boats.

[iduff]

Originally Posted by Cpt Mark

You need to call a Yamaha dealer and go to the service department.

I just did this yesterday. I have a Honda 8hp I wanted to upgrade to a 9.9 or 10. All the specs looked the same, cc, weight, bore, stroke etc. What wasn't the same was the cam shaft. I looked up part numbers and photos. very different. had that been the same, then it would have been a new carb, $129, new prop, and probably a new CDI.

@Cpt Mark, care to share any details? I have a Honda 8 that i've been pondering how to do the same.

[hirondeller]

The 'new' (EFIs are 2015+) are 'upgradable'. The 9.9, 15, 20hp motors look identical under the cowl, I checked this at a boat show. These are computer controlled motors. The upgrade looks like a you have to enlarge a restrictor plate in the throttle body (by drilling) and install a new engine computer.


Here is a 'comments quote" from the video below: "The ONLY part numbers that are exclusive to the 9.9 are the restrictor plate and the ECM. After doing the change, the ONLY part numbers different between the 9.9 and the 20 are the decals!"


This video shows how:

https://www.youtube.com/watch?v=NGy6M-FYE9g

[sailingharry]

Originally Posted by donradcliffe

I did my own upgrade to that engine. Turns out the biggest difference was that the throttle cam on the 9.9 only open the throttle half way

Can you give any more details on this? I have a 9.8 tohatsu two-cycle. Is that the same as the 9.9? And what did you upgrade it to? At 57 lb, I doubt mine can produce any more horsepower. But it would be nice if it could!

[donradcliffe]

Originally Posted by sailingharry

Can you give any more details on this? I have a 9.8 tohatsu two-cycle. Is that the same as the 9.9? And what did you upgrade it to? At 57 lb, I doubt mine can produce any more horsepower. But it would be nice if it could!

The 9.8 was a smaller block engine and I believe it was already at the top of its HP range.

[zephyr4]

I have a recent Yamaha 4-stroke caburated 9.9 and would love an extra 50% hp in the same weight.

Bad news for the original poster: The Yamaha 4-stoke 15 hp is a larger displacement motor than the 9.9 hp. Unlike some of the motors other posters have mentioned,the 9.9 is not based on the same short block as higher hp motors and can not be upgraded to 15 hp by changing a few inexpensive parts.

I do feel your concern with weight: I bought a Yammie 9.9 instead of 15 for exactly that reason. What I don't understand is why people buy the 8 hp motor. Same weight, similar cost, less mojo.

[rslifkin]

Originally Posted by zephyr4

Bad news for the original poster: The Yamaha 4-stoke 15 hp is a larger displacement motor than the 9.9 hp. Unlike some of the motors other posters have mentioned,the 9.9 is not based on the same short block as higher hp motors and can not be upgraded to 15 hp by changing a few inexpensive parts.

I do feel your concern with weight: I bought a Yammie 9.9 instead of 15 for exactly that reason. What I don't understand is why people buy the 8 hp motor. Same weight, similar cost, less mojo.

The 8hp is likely offered (and purchased) for use on boats that are rated for a max of 8hp. If you want the most power the boat is rated for but want to stay within the ratings, that's the only choice. Otherwise you either over-power it with a 9.9, or you save some weight and step down to a 6.

[Cpt Mark]

Originally Posted by iduff

@Cpt Mark, care to share any details? I have a Honda 8 that i've been pondering how to do the same.

Honda service guy sent me to boat parts.net I believe. In there, you can find your exact engine and see what parts it uses vs what parts on the larger engine, in my case, 9.9 or 10. The cam shafts are of a different design so I doubt they would be interchangeable. Had they been the same, then it would have probably been a new carb and possibly cdi. Carb for fuel flow and cdi for timing etc..

[campbdon]

Has anyone here uppowered their Suzuki DF9.9B to either 15hp or 20hp? Apparently it can be done by opening up the restrictor plate slightly (for approx 15hp), or by replacing the DF9.9 ECM and restrictor plate with the DF20A ECM and flame arrestor. How large to make the RP hole (for 15hp) , and/or what part# ECM (for 20hp) to swap in for a 2021 DF9.9B elect start model?