Tohatsu 25 to 30 hp difference

[denlyn]

Has anybody checked out the difference in performance after changing a 25 hp Tohatsu to 30 hp? Is it worthwhile?

 

[TOHATSU GURU]

Re: Tohatsu 25 to 30 hp difference

The only difference is the carburetor manifold gasket. It's a five hp increase for the cost of a cheap gasket. What's not to love about that?

 

[denlyn]

Re: Tohatsu 25 to 30 hp difference

What I was wondering is if there is a noticeable difference in the perfomance between the 25hp and the 30hp. This would be on a Alumacraft 16.5 ft Yukon. Thanks

 

[Graham Anderson]

Re: Tohatsu 25 to 30 hp difference

Alvin and others.

Just a couple more questions re 25 - 30 conversion plus an alternator question. I am down in the Keys and wonder if most Tohatsu dealers are familiar with this conversion? There is no re-jetting of the carb or anything else to do? I have a new 25 and am not worried about warranty.

Also, would this 25 manual start have an alternator and if so, what do I need to charge a small 12v battery to run the trim tabs and possibly a power pole and GPS.

I am told the Yamaha 25 manuals have a 6 amp alternator but would rather stick with the Tohatsu and crank it up to 30 hp.
Thanks for any and all answers.
Graham

 

[Graham Anderson]

Re: Tohatsu 25 to 30 hp difference

Fo5 und the answer to the 25 hp -30 hp conversion re carb jets in an old thread but would still like to know
if the motor has an alternator or how do I add one.

Also, would I get much advantage from a SS prop compared to the factory prop. I have the motor on
a 16 hells bay waterman which weighs 325 or so. I can
get over 30 mph in good conditions, but you know how it is. Faster with the same is always better.

 

[steelespike]

Re: Tohatsu 25 to 30 hp difference

First it is considered poor form and confusing to post into an existing question.
But first a gps measured speed of 30 is pretty good
to answer your question yes a prop change could help but you need to know what prop you have now and what wot rpm you are running.Should be a number on the prop -- X --.
Before changing props check the verticle height of your motor.Antivent plate should be about even with the bottom of your boat.Then raise the motor 1/4 inch at a time using 1/4 inch sticks until just before ventilation becomes a problem.
If you can gain an inch it could give you 2 to 3 mph.
Also carefully adjust the trim.If one notch doesn't seem enough and the next seems too much you can make or buy wedges for between clamp and transom to give you
half a notch.Just be sure the clamp has a good bite and water is being pumped.
Once you have this all set then you can go over to the prop forum with the details and get info about adding a prop to give more speed and bite and you may be able to tweak trim and height even more.Keep in mind that usually a prop picked for speed may limit load pushing ability.

 

[TOHATSU GURU]

Re: Tohatsu 25 to 30 hp difference

It is just a manifold gasket difference between the 25 and 30. No difference on the carb at all. Tohatsu/Nissan has never advertised to it's dealers what can be done to make one into another. IE They don't tell you what the differences are between one model and another that share a common CID. It's just something you either know or more likely...Don't. Propping is one of those things that people tend to over think based on advice from people who got advice from people who got advice from people who got advice from people...Get the point? Basically propping is trial by error with a huge slop factor as to what is "perfect". If you are happy with the performance you have...Stop and be happy. You can acheive modest results in performance by small changes in pitch. But, you usually gain in one area to lose in another. The only time you will see a hole shot increase and a top end increase is if your were propped less than "perfect" before. Stainless allows you to stay at the same pitch(and not lose hole shot) and increase top end...A little. Little being 1 to 3 mph. Dropping $225 to $400 for a 1 mph increase is dumb, but we sell a lot of props to people who feel differently.

A lot of people have different opnions than I do on propping...So, based on individual circumstances you might see a huge improvement, no improvement or totaly FUBAR your engine. Steelspike's advice is as accurate as you are going to find and I would urge you to play with the engine mounting before you start buying props.

The manual start 25-30 frame would require a alternator coil, rectifier, mounting harware and wiring harness. Available from any Nissan or Tohatsu dealer.

 

[drgmaps]

Re: Tohatsu 25 to 30 hp difference

A Tohatsu America Corporation employee said (in an email) both the restrictor gasket and a timing adjustment are what differentiate the 25 and 30 hp egines (25C3 vs. 30A4).

Is this the case? Or is no adjustment to timing really necessary when replacing the manifold gasket when converting 25 to 30 hp?

 

[TOHATSU GURU]

Re: Tohatsu 25 to 30 hp difference

If it is a C3 you do need to adjust the timing to meet the A4 standard. The 30A4 can run 5 degrees more at BTDC. Do you have to?....No, but to achieve the most you possibly can out of the engine you can.

 

[drgmaps]

Re: Tohatsu 25 to 30 hp difference

What is the procedure for adjusting timing on a 25C3 to fully convert it to a 30A4 after changing the manifold gasket?

 

[TOHATSU GURU]

Re: Tohatsu 25 to 30 hp difference

That procedure is described in detail in your service manual. It takes about 30 seconds to do.

 

[kjellejon]

Re: Tohatsu 25 to 30 hp difference

on the 2007 mfs 25/30

http://www.onlineoutboards.com/30hp_4stroke_tohatsu_outboard_motor.html

"The 25/30hp outboards share the same engine block with the 30hp featuring an upgraded ECU (engine control unit) and advanced ignition timing which increases the horsepower and enhances performance. "

Is it really any difference in the ecu? Is it impossible for me to improve performance on my 25 hp version. What would happen if i altered the ignition timing only?

 

[TOHATSU GURU]

Re: Tohatsu 25 to 30 hp difference

The only way to turn your engine into a 30 is by changing out the $1000.00 plus ECM. Any further discussion on this is pointless.

 

[pvanv]

Re: Tohatsu 25 to 30 hp difference

Alvin and others.

Just a couple more questions re 25 - 30 conversion plus an alternator question. I am down in the Keys and wonder if most Tohatsu dealers are familiar with this conversion? There is no re-jetting of the carb or anything else to do? I have a new 25 and am not worried about warranty.

Graham

Graham,
The new fuel-injected 25's use a specific ECU, as noted above by TG. To change that to a 30 would require a new, pricey, ECU. The 25/30 mods apply only to the old carbureted models.