Tohatsu 25hp and Tohatsu 30hp...what's the difference?

[Greenheart]

Apparently...NOT MUCH.

I was surprised how little. The specification page for the 25hp model is here... http://www.tohatsu.com/outboards/25_4st_spec.html

...and here is the page for the 30hp... http://www.tohatsu.com/outboards/30_4st_spec.html

...they're basically identical, except for one thing...peak engine speed is 250RPM higher for the 30hp.

Is that it? Could one make changes to the throttle control on the 25hp motor, which would allow it to rev higher, thereby safely increasing power by 20%?

Is there any downside to an engine having the option to rev a bit higher? Would there be any downside to buying the 30hp but never revving it to more than 25hp?

It seems that all through the range of outboards, there are examples of exact same engine blocks with differing outputs caused only by the rev-rates each is limited to.

 

[Lakesailor]

Sometimes it is as simple as a throttle stop. Sometimes jets in the carb. Sometimes a whole load of things.
You have to take it case by case.

 

[Beyondhelp]

Probably only the carb.

The Tohatsu/Mercury 4-5-6 HP are the same kind of thing. IDENTICAL engines but in that case only difference is the carb and about £2-300 in price.. You can buy a 4hp and fit a 6hp carb and save a few hundred ££. Which is exactly what I did.



The difference is quite clear in this case, the carb cost about £60 and the difference in prices new is many times that... Crazy but true. Oh and it made a hell of a difference to the torque and power the little engine produces.

 

[Beyondhelp]

It looks like these could be EFI engines, in which case the difference is in the ECU, and the way its programmed, since it wont have a carb.

 

[TQA]

Nope they have carbs. I am 99% certain that it will be just the carb that is different. Check the online spares site.

 

[Beyondhelp]

I did on the model numbers linked from the first post.. The 2014 models are EFI. I guess they just changed over.

 

[Ripster]

Probably only the carb.

The Tohatsu/Mercury 4-5-6 HP are the same kind of thing. IDENTICAL engines but in that case only difference is the carb and about £2-300 in price.. You can buy a 4hp and fit a 6hp carb and save a few hundred ££. Which is exactly what I did.

View attachment 44290

The difference is quite clear in this case, the carb cost about £60 and the difference in prices new is many times that... Crazy but true. Oh and it made a hell of a difference to the torque and power the little engine produces.

I remember doing this on motorbikes. Derestricting the engine performance by bolting on a bigger carb and jetting accordingly, but often the exhaust would need modding too. In your case with the Tohatsu, did you literally just buy a complete carb assy from the dealer and bolt it on - no other mods at all on the 4hp? And it all runs fine?

 

[Beyondhelp]

I remember doing this on motorbikes. Derestricting the engine performance by bolting on a bigger carb and jetting accordingly, but often the exhaust would need modding too. In your case with the Tohatsu, did you literally just buy a complete carb assy from the dealer and bolt it on - no other mods at all on the 4hp? And it all runs fine?

Yep that is EXACTLY what I did. Except I ordered the carb from the US, as it was cheaper. It took a while to arrive, and made an immediate difference. No disadvantages here. It just works fine, there are not that I can see from looking at parts listings any other differences. Its quite clear from the 4hp carb that it is horrendously restrictive.

The engine is used on a wetline 230 tender, and as backup. It would not plane at all with the 4hp carb. It plains easily with the 6hp, and is quite good fun !

 

[Greenheart]

Thanks for all replies. My enquiry was a purely theoretical one, relating to the lightest possible solution for catamaran auxiliaries.

I know having a diesel in each hull is well thought-of for the reliability and redundancy, but their weight and use of space must make an outboard very tempting...

...especially when two and even three cylinder outboards pack twice or thrice the power into much less weight, in a position that won't monopolise hull space.

 

[TQA]

I did on the model numbers linked from the first post.. The 2014 models are EFI. I guess they just changed over.

I guess shipments have not reached the Caribbean as they are selling carb versions.

 

[grafozz]

Probably only the carb.

The Tohatsu/Mercury 4-5-6 HP are the same kind of thing. IDENTICAL engines but in that case only difference is the carb and about £2-300 in price.. You can buy a 4hp and fit a 6hp carb and save a few hundred ££. Which is exactly what I did.

View attachment 44290

The difference is quite clear in this case, the carb cost about £60 and the difference in prices new is many times that... Crazy but true. Oh and it made a hell of a difference to the torque and power the little engine produces.

is this 2 stroke or 4 stroke ?
if its 4 can the same theory be used on 2 stroke ?

 

[Davy_S]

A different engine I know but, when you compare a 25hp Honda and 30hp Honda, both use 3 carbs per engine, the 30 revs higher, to gain the extra 5hp. It is not so simple though! the carb jets are different, but so is the inlet manifold. making it too expensive to consider.

 

[Beyondhelp]

is this 2 stroke or 4 stroke ?
if its 4 can the same theory be used on 2 stroke ?

4 stroke. Dont know about others im afraid. Would need to loom at the parts listing

 

[catalac08]

I had my 25HP Tohatsu uprated to 30HP-there is a restrictor plate at the carburettor gasket that is merely taken out of the 25 to do the upgrade. I do not recall a bigger carb jet being involved.

 

[Greenheart]

Most interesting, Catalac...I'm assuming the Tohatsu is your auxiliary, centrally mounted? Is the long shaft, long enough? Is the gearing suitable for displacement-speed applications?

I read that the 25/30hp engines could be fitted with props up to 14" diameter - pretty good for thrust I'd think, assuming there's enough torque to turn it. What diameter is yours?