Are the 9.9, 15, and 20 HP Tohatsu all the same engine?

[The Rooster]

I'm looking at getting a small pontoon boat, a Paddle King, and the dealer offers them with Tohatsu engines. I'm comparing engines and I see the 9.9, the 15, and the 20 HP models all have the same cc rating, same bore and stroke, same RPM range, and same gear ratio. What makes the HP difference?

I noticed the same thing between the 8 and 9.8 HP motors too. Same engine it seems.

What really throws me off is comparing the 9.8 vs 9.9 HP motors. They are not the same size, bore, stroke, or otherwise, but are within 0.1 of being the same output? How?

[BassmanRudy]

Looking at specs the 9.8(81.5) is 13lbs lighter than the 9.9(94.7) and has 124 Less cc displacement(333cc to 209). The 9.9 can also come in a "sport" model with power trim and a 4 blade prop.

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[Princeton_Man]

I don't know anything about the Tohatsu outboards. I do know that just like automotive motors, outboards can share the same displacement but have different horsepower. In newer motors, the different horsepower is obtained through various computer tunes and sometimes other components. In carbureted outboards it was done with larger carburetors, larger jets, different reed valves, etc.

There are generally other differences in the drive trains like heavier/stronger shafts and gears that come with the higher horsepower.

[The Rooster]

I found a video where a guy showed how to convert a 9.9 Suzuki to a 20 HP. All he did was change the (ECM?) and the air intake restrictor from just a cover with a small hole to a wide open grill. Otherwise he said it was the same motor. I guess that's how it would be with these too, something similar.

At any rate I'm going with the 9.9 HP with EFI. It's just a small pontoon boat, the whole thing is just 13' long with a 7x10 deck. Weighs 660 pounds. A 9.9 should be all I'd need or want.

[Princeton_Man]

Be sure to post a "How to" here if you ever upgrade it to a 20.

[The Rooster]

Be sure to post a "How to" here if you ever upgrade it to a 20.

Well........I done upgraded it to a 20 before I even bought it, LOL! It's been a couple of months since I made this post but since then I ordered the boat and am still waiting for it to be built. Im supposed to take possession of it either in late August or early September. But since the price difference between the 9.9 and the 20 HP motors was just $500 I figured go ahead and get the bigger one now. So I opted for the 20HP.

[BassmanRudy]

Good deal! Now you won't "wonder" what could have been lol.

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