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Well I completed the conversion of my Nissan 40hp NS40D2 to a 50 hp NS50D2 and I thought others might want to know how it was done.

I purchased a parts catalog on eBay that detailed the NS40D2 and NS50D2. After reviewing the catalog in detail the NS40D2 is a detuned NS50D2 block and the only difference between the two models is:
1) Carburetors (larger barrel and jets and butterfly opens fully on the 50 hp model)
2) Intake manifold (larger holes to match larger carburetor barrels)
3) Reed valve assemblies (turns out the only difference here is the plates that limit how far the reeds can open - plates allow reeds to open farther on 50 hp model)
4) Air silencer (larger holes to match larger carburetor barrels)
5) Throttle cam (different shape to open butterfly fully on 50 hp model)
6) Spark plugs (BR8HS-10 for 50 hp model vs BR7HS-10 for 40 hp model)
7) Timing link length adjustment (same part but adjusted shorter for 50 hp model and thus timing is more advanced compared to the 40 hp model)

I had concern that the engine block porting might be different between the NS50D2 and NS40D2; however, I confirmed with Tohatsu directly that the blocks are the same between the two models and that the only differences were in fact 1 thru 7 above

It costs about $800 to purchase the parts from Tohatsu; however, I got lucky and found them used locally for $300. I also purchased a carburetor rebuild kit for $100 so my total cost was $400 - about half price and not bad for a 25% power upgrade.

The old carburetors cleaned up really nice and the project was pretty straight forward. Once I had all of the new parts installed I re-adjusted everything to factory NS50D2 specifications (carb synchronization, timing link, throttle link, oil mixer link, idle mixture, and idle screw settings).

I posted pictures of the work on my personal page.

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Your boat looks really nice on your personal page. It looks like you fixed the engine mount height (and odd double bolts in the top of the bracket). I did a conversion from a OMC 60 to 70 (by looking at a parts catalog like you did) and the only change was the carbs. The difference for me was worthwhile.

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Dave - Thanks. Yes I did correct the motor mounting issue. Plan to update personal page pictures once the weather warms up. I'm glad to see it was a worthwhile upgrade for you. I am expecting top speed ~40mph+ (previously 35mph at 40hp and before correcting motor mount issue).

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I found a place online that can reproduce discontinued decals: http://garzonstudio.com/outboard/niss...issan.html.

They are reproducing a Nissan NS50D2 50 hp decal for my motor hp upgrade project. Thought others might find this resource useful.

Also, I relocated the pictures for this thread from my personal page to a project album: http://www.whalercentral.com/userphot...lbum_id=65

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The reproduction Nissan 50 hp decal arrived from Garzon Studio and I installed it. The quality of the work is outstanding. I added a picture to the project album: http://www.whalercentral.com/userphot...to_id=1759

Last item to address is the prop. Was previously running a Solas New Saturn stainless 12 pitch prop (part #5331-114-12) and the engine (40hp at the time and mounted all the way down) reached 5700rpm and 34-35mph (GPS). I'm now running 50hp and the motor has been raised 2 holes. I was thinking of going up to the Solas New Saturn stainless 14 pitch prop (part #5331-111-14). Engine gear reduction ratio is 13:24. Anyone have suggestions about the best choice?

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I don't know if its the right prop for your setup (ie no experience, my experience is with stiletto & OMC SS props)

Going up 2" to a 14P prop should be the right pitch change for going from 40 to 50 hp. Based on your experience with the 12P version, if the motor can spin to 5700 rpm, the boat should be doing about 39-40mph.

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dgoodhue - Thanks for the input. Selecting a prop is a challenge. Always an educated "best guess" based up the data one has.

Does anyone have any thoughts/opinions about Solas vs Silletto vs other bands of stainless props?

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I splashed the boat today (purchased the Solas 14p prop) and I'm happy to report I'm seeing 39 mph (GPS) and an outstanding hole shot. The boat also handles really really well.