What is the difference between a 15HP and 20HP tohatsu?

R

RRitt

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I can't find anything different between these two engines other than the carberator.
The manifolds, ignition, block, head, and crank are the exact same part #. Even the factory prop is the same.

It looks like Tohatsu puts a smaller carb on a 20HP and sells it for $500 less. You can buy the 20HP carberator for under $250.

What am I missing?
 
ajgraz

ajgraz

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Re: What is the difference between a 15HP and 20HP tohatsu?

5HP









(Sorry, couldn't resist :p )
 
M

mickjetblue

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Re: What is the difference between a 15HP and 20HP tohatsu?

I have an 18, so I must have the best of two worlds, with a slight advantage to the high end.

:D

Actually, try moving this to the Honda and Tohatsu motor forum,
and Tohat Guru will probably respond with the answer.

Good luck!

:)
 
O

omar h

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Re: What is the difference between a 15HP and 20HP tohatsu?

you're right, they're the same outboard except for the carb. On the other hand, I might be mistaken but if I recall correctly, it's against federal law to tamper with changing carbs or any of the other specs., Why? I don't know...
 
Frank Acampora

Frank Acampora

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Re: What is the difference between a 15HP and 20HP tohatsu?

The old Chryslers were like that--multiple horsepower rating from the same block: 20, 25, and 35; 70, 75, 85, and 90 for example. Carbs were a different size and jet for each horsepower. BUT: While the block, head, manifold, crank, and pistons were the same externally, porting was different inside. So while your 20 and 25 may use all the same part numbers, there is a decent chance that the port timing is different. A larger carb MAY give more horsepower, but then again, it may not. So, don't be surprised if a carb change is disappointing.
 
jay_merrill

jay_merrill

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Re: What is the difference between a 15HP and 20HP tohatsu?

omar h said:
you're right, they're the same outboard except for the carb. On the other hand, I might be mistaken but if I recall correctly, it's against federal law to tamper with changing carbs or any of the other specs., Why? I don't know...
Click to expand...

Never heard that one, but if its true, I'd take aguess that envinronmental issues are involved.
 
pvanv

pvanv

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Re: What is the difference between a 15HP and 20HP tohatsu?

RRitt said:
I can't find anything different between these two engines other than the carberator.
The manifolds, ignition, block, head, and crank are the exact same part #. Even the factory prop is the same.

It looks like Tohatsu puts a smaller carb on a 20HP and sells it for $500 less. You can buy the 20HP carberator for under $250.

What am I missing?
Click to expand...

Depends on the precise model. The 15C and 20C differ by carb. The 15A and B were a different block from the C.

OB manufacturers build the motor lineups in "families" of block/frame sizes. In the Tohatsu/Nissan/Mercury 4-stroke line, the 2.5/3.5, 4/5/6, 8/9.8 (merc calls it the 9.9), 15/20, and 25/30 are designed that way. In essence, the smaller hp motor is a de-tuned version of the larger brother. This is to accommodate boats or bodies of water with specific hp limits. The de-tuning can be done in a number of ways, from mechanical differences, to timing, to fuel system, to ECU.
 
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TOHATSU GURU

TOHATSU GURU

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Re: What is the difference between a 15HP and 20HP tohatsu?

Like Paul said, just the carb on the 15C/20C frame.
 
S

Star

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Re: What is the difference between a 15HP and 20HP tohatsu?

I own a 15hp Mercury 4 stroke. I belive that tohatsu has a cam change but I am not sure that they are interchangable. They use the same block from 9 to 30 HP but also use injection on the 30. Good luck would like to hear how you make out. The timing and max rev unit must also be different on the bigger motors.
 
pvanv

pvanv

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Re: What is the difference between a 15HP and 20HP tohatsu?

No. You can't put 3 cylinders into a 2-cylinder block (by ordinary means). Of the current 4-strokes (Tohatsu makes the Mercury powerheads), the lineup is 2.5/3.5 on one frame/block, 4/5/6 on another, then 8/9.9 on one common block/frame, 15/20 on another, and the 25/30 EFI 3-cylinder on the last.
 
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TGuy

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Re: What is the difference between a 15HP and 20HP tohatsu?

Star said:
I own a 15hp Mercury 4 stroke. I belive that tohatsu has a cam change but I am not sure that they are interchangable. They use the same block from 9 to 30 HP but also use injection on the 30. Good luck would like to hear how you make out. The timing and max rev unit must also be different on the bigger motors.
Click to expand...

The same block from 9.9hp to 30hp???? How do you figure? The 25/30hp is a 3-cylinder motor. The others are 2-cylinder.
 
R

RRitt

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Re: What is the difference between a 15HP and 20HP tohatsu?

TOHATSU GURU said:
Like Paul said, just the carb on the 15C/20C frame.
Click to expand...

so if i buy a current block 15hp then i could get a 5HP boost from changing the carb? I have a teenager and want the boat to be as slow as possible. But it also needs to be fast enough to dash home ahead of a storm. Being able to buy a 15 with easy upgrade to 20HP is perfect.
 
T

TGuy

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Re: What is the difference between a 15HP and 20HP tohatsu?

You could, but you'd also be breaking the law. EPA regulations make it illegal to modify an EPA approved motor in any way that would change the emissions that it was originally approved to meet. And boosting a 15hp to a 20hp would certainly change it's stated emissions. So when the EPA police :) come and check your motor you'd be subject to a hefty fine...and if a dealer did the modification, they would be fined as well. My advice is to make sure you run like a scaled dog when the EPA police show up at your doorstep. Or blame it on your teenager and let them take the rap. LOL :D
 
R

RRitt

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Re: What is the difference between a 15HP and 20HP tohatsu?

TGuy said:
You could, but you'd also be breaking the law. EPA regulations make it illegal to modify an EPA approved motor in any way that would change the emissions that it was originally approved to meet. And boosting a 15hp to a 20hp would certainly change it's stated emissions. So when the EPA police :) come and check your motor you'd be subject to a hefty fine...and if a dealer did the modification, they would be fined as well. My advice is to make sure you run like a scaled dog when the EPA police show up at your doorstep. Or blame it on your teenager and let them take the rap. LOL :D
Click to expand...

So ... if I ever build my dream engine would the EPA police come get me? It's an old Johnierude 20" tiller gearcase & pan modified so that an 18HP lawnmower engine just bolts right on.
 
TOHATSU GURU

TOHATSU GURU

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Re: What is the difference between a 15HP and 20HP tohatsu?

It wouldn't be a violation of the EPA regulation...In theory:) The engine was designed and built as a 20 hp and is in compliance as a 20. Now, that's something of a shift from the interpretation that we used to have which was any change was a violation. But, the present interpretation is that anything that does not actually take the engine out of the approved emissions spec is OK.
 
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becxlt

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Re: What is the difference between a 15HP and 20HP tohatsu?

its really just that easy to pick up and extra 5 hp ? I own a Toahatsu 15MFSC and would also like to do this mod . Is there any other tuning required ? :eek:
 
pvanv

pvanv

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Re: What is the difference between a 15HP and 20HP tohatsu?

becxlt said:
its really just that easy to pick up and extra 5 hp ? I own a Toahatsu 15MFSC and would also like to do this mod . Is there any other tuning required ? :eek:
Click to expand...
If you have a tiller model, you would order 3BJ031000M CARBURETOR, F20C (MF/EF) $232.30; If yours is remote, the correct 20 hp carb is 3BJ031330M CARBURETOR, F20C (EP/EPT) $232.30. Either carb is available from any dealer, including me. No other modification is needed.
 
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