Horsepower ratings

[whfmznb]

I'm looking at the Nissan/Tohatsu outboards. I'm ready to get the 18hp and then realize that the 9.9 is the exact same motor. Weight, displacement, bore & stroke, gear ratio,....all the same.<br />Please tell me what they do to double the HP.<br /><br />Thanks....

 

[steelespike]

Re: Horsepower ratings

That must be a really heavy 9.9 or a really light<br /> 18.<br /> Dont know specifically on your motor but Im betting it is everything from a carb change to<br />different porting,reed valves etc.Pretty major stuff.Maybe someone will follow up with more specifics.

 

[whfmznb]

Re: Horsepower ratings

It would seem so to me too...and we can add the 15hp version to the list. It says they all weigh 114.4lbs.

 

[Red Rider]

Re: Horsepower ratings

I don't know for sure about that make of motors, but the HP difference on most of the motors that are the same size is the results of different RPM's of the engines. They accomplish this by a varity of means. <br /><br />To reduce the HP they reduce the RPM by such tricks as: A smaller carberator, A restricter plate behind the carberator, On older engines the exhaust may have been restricted, a stop in the linkage that keeps it from opening all the way, smaller reeds, a reed stop (so they can't open as far), etc.<br /><br />Changing jets on the carb will not give you the higher HP engine, but changing the carb and reeds usually will, especially on later model engines. On the later model engines, due to fuel economey and emmisions they don't restrict the exhaust system to reduce the HP.

 

[kend20gw]

Re: Horsepower ratings

I can't swear this is correct but thought I'd share it with you:<br /><br />> This is taken from the rec.boat.racing.power newsgroup... and to think,<br />> all that wasted money on mods ect.. LOL<br />><br />> Subject:<br />> Re: MERC HORSEPOWER DIFFERENCE<br />> Date:<br />> Wed, 02 Dec 1998 03:22:28 GMT<br />> From:<br />> TerryBear <terryb_1998@hotmail.com><br />> Organization:<br />> Bell Solutions<br />> Newsgroups:<br />> rec.boats.racing.power<br />> References:<br />> 1<br />><br />> This also applies to most other outboards as well. Next time you get a<br />> chance<br />> check out an Evinrude 9.9 and a 15 hp. You will discover after searching<br />> dilligently through the parts catalogs that the only difference is the<br />> carburation. IE ... buy the carburator for the 15hp ... transplant it to<br />> the 9.9 hp and viola ... a 15hp at a much better price... all the<br />> manufacturers do this. The same applies to skidoos and seadoos as<br />> well.... Must be the same family of engines though. for a real<br />> hourspower increase try changing the reed valves to a performance set. I<br />> gained 9hp on a 40hp evinrude by simply changing the metal reeds for the<br />> high performance plastic reeds..<br />><br />How 'bout it guys, true? Ken

 

[Trevor]

Re: Horsepower ratings

Hey guys I recently up tuned my Yamaha 9.9 to 15hp all I had to do was change the main jets in the carb and the read valve on some brands you would have to also eather change the exhaust restrictor or just remove it. <br />what a difference I have it on a 9'6 zodiac and can pull a 170lbs guy on a tube behind it !!!

 

[mudbass1]

Re: Horsepower ratings

Hello<br /> The difference is the carb,Fuel pump, and the RPM,s. I had the 9.9 Loved it but due to the cost of the parts I traded it in for the 18hp. Wow what a difference.They are Very Good engines for their price.I've had one of the 2 strokes since the early 80's not one problem out of it yet! and no telling how many hours I have on it? It has gone all the way down the Sabine river to Toledo Bend and back Hundreds of times over the years.They are Real Good engines.I've had it on more boats because the boats tore up one the hard run,but not the engine. Hope this Helps.