Tohatsu 90hp lower unit gear upgrade to the 70hp lower unit gear question

sgrem

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I have heard that it is a good gain to put the 70hp lower unit gears of 2.3:1 to replace the lower unit gears of the 90hp lower unit gears 2:1. I have a 1998 70hp that i have replaced with a 2003 90hp TLDI. I am keeping the 90 but if the lower unit gears of the 70 is a good upgrade i would like to swap them before i sell the 70. Can anyone confirm this and what is the best way to go about this?

I have both lower units dropped and the 90 has a larger driveshaft. is there a way to just swap driveshafts?
 

TOHATSU GURU

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Re: Tohatsu 90hp lower unit gear upgrade to the 70hp lower unit gear question

Drop the idea.
 

sgrem

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Re: Tohatsu 90hp lower unit gear upgrade to the 70hp lower unit gear question

thanks so much for the reply.....can you expand a little. .....would be much appreciated so i can get some sleep....
 

TOHATSU GURU

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Re: Tohatsu 90hp lower unit gear upgrade to the 70hp lower unit gear question

Drop the idea because it will not work.
 

sgrem

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Re: Tohatsu 90hp lower unit gear upgrade to the 70hp lower unit gear question

Now im confused....manufacturer says it will. Here is what i have been able to find out.
Forever the equally equipped boat with a nissan/tohatsu 70 would outrun the 90 all day. Tohatsu got sick of other manufacturers 90's being so much faster and the tohatsu 90 was more of a commercial motor to carry a bunch of weight. Dealers started upgrading the lower unit gears in the 90 hp to the 70 hp lower gears and make a performance 90. NOW tohatsu got smart and started doing it from the factory in their 2011 line up of larger 90/115/140 motors.

So the gears will change out case to case and from what i understand on pre 2011 tohatsu/nissan 90+hp engines you want the 70 hp lower gear set for performance.
 

TOHATSU GURU

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Re: Tohatsu 90hp lower unit gear upgrade to the 70hp lower unit gear question

And it still will not work. The manufacturer, Tohatsu, has never said it will work. But, if you have your heart set on wasting your money and time...By all means ignore what I said and do it.
 
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