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Old 07 July 2010, 08:08   #1
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need for speed

hi all, i'm after a bit more power from my 18hp tohatsu 2 stroke, to tow toys etc.

I have been told by my local mechanic that it is possible, by tweeking the carb etc to upgrade the motor to nearly 25hp, but he reckons that i'll use upto 10% more fuel.

The cost to do this including the service would be 75.

The other option would be to change the prop to a different pitch.
We use our 3.8m inflatable for fishing and towing ringos and was wondering what you all think would be my best option. (do i go for a higher or lower pitch, stainless or aluminium).

thanks in advance
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Old 07 July 2010, 12:39   #2
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It'll only use 10% more fuel if you open the throttle that far.
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Old 07 July 2010, 13:08   #3
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id say get the job done
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Old 07 July 2010, 13:21   #4
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Quote:
Originally Posted by uny1965 View Post
hi all, i'm after a bit more power from my 18hp tohatsu 2 stroke, to tow toys etc.

I have been told by my local mechanic that it is possible, by tweeking the carb etc to upgrade the motor to nearly 25hp, but he reckons that i'll use upto 10% more fuel.

The cost to do this including the service would be 75.
Thats quite a "bold" claim (40% more power just from tweaking things). To get 25% more power from my engine I need to replace the carbs (not just tweak) and replace part of the exhaust. That would cost significantly more than 75. However since a service would cost about that anyway I'd suggest you go ahead - but don't get too hopeful. I'd have thought if he increases your power by 40% the fuel consumption at full throttle would go up likewise - unless he's found a way to make your engine more efficient. Or is he suggesting that it will use 10% more power to deliver the same speed?

Quote:
The other option would be to change the prop to a different pitch.
We use our 3.8m inflatable for fishing and towing ringos and was wondering what you all think would be my best option. (do i go for a higher or lower pitch, stainless or aluminium).
that all depends on what the current prop is delivering at full throttle, if you've got enough "grunt" to get on the plane when towing etc. indeed - if he does get you an extra 40% in HP then you may well need to reprop anyway.
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Old 11 July 2010, 13:53   #5
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Quote:
Originally Posted by uny1965 View Post
hi all, i'm after a bit more power from my 18hp tohatsu 2 stroke, to tow toys etc.

I have been told by my local mechanic that it is possible, by tweeking the carb etc to upgrade the motor to nearly 25hp, but he reckons that i'll use upto 10% more fuel.

The cost to do this including the service would be 75.

The other option would be to change the prop to a different pitch.
We use our 3.8m inflatable for fishing and towing ringos and was wondering what you all think would be my best option. (do i go for a higher or lower pitch, stainless or aluminium).

thanks in advance
If it's a newer model M18-E2, cannot update a Tohatsu 18-2 T to 25 HP. 18 is 300 CC and 25 is 430 CC, different engine heads, carbs and parts. Will need to buy a new one. Could play with pitch a bit, will need a tacho and perform a wot test to read current rpm with given prop to see max rpm achieved.

Happy Boating
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Old 11 July 2010, 15:14   #6
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For 75, go for it, but dont expect too much. The 18 hp engine is said to be sensitive to pitch, most likely you need 2 props, one lower pitch for towing rings and another for other boating. Increase in consumption will be proportional to increase in power. It is possible to take 25 hp out of 300 CC engine, but not sure if 75 is enough for that.

I have the 25 hp on my bombard, 11 pitch prop. When towing, the smart tabs helped a lot, helping to get the boat on plane at lower speed without huge bow lift. Noted also a minor loss on top speed. Another thing that have a big impact on towing speed is to have a correct presure in the air floor, the bigger the load the more You will loose if floor is too soft.

In my opinion the 25 hp is slightly to heavy to handle, its a pig to move from the car to the transom if alone. The long rig model weight like 55 kg, one day will most like hurt my back...In that respect the 18 hp is a much better choice. Good luck
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