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#1
10-30-2006, 05:51 PM
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WOT speed on a '83 20' SF w/200
I've got an '83 20' SF with a 99 Merc 200. I've been playing with props and setup and can't get it to go more than about 46 mph gps. Shouldn't this be a 50+ mph boat?
Thanks, Dave
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Blue Heron Boat Works Reinventing the wheel, one spoke at a time. 
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#2
10-30-2006, 07:07 PM
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Re: WOT speed on a '83 20' SF w/200
The appropriate prop needs to be installed to acquire 100% of the maximum rpm as specified by the motors OEM with a light load. That said, yes, it should be a 50 MPH boat. There are a number of factors that could slow her down (excessive weight, t-top, poor tune-up, hull condition, etc.), but the prop thing is a given.
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Otto And yes, I still believe in the four boat theory...
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#4
10-30-2006, 10:12 PM
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Re: WOT speed on a '83 20' SF w/200
Quote:
The boat came with the Merc already on it. If I were starting from scratch, I might go with a Yami. If top speed were my only consideration, I'd stick with the Merc. All that being said, a 175 Yami ain't gonna be faster than a 200 2-stroke of any make. Horsepower is horsepower, it don't matter what color the engine is.
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Blue Heron Boat Works Reinventing the wheel, one spoke at a time.
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#5
11-16-2006, 02:54 PM
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Re: WOT speed on a '83 20' SF w/200
"horsepower, it don't matter what color the engine is."
Shame on you Blue Heron; you obviously know better. For one thing Horsepower ratings are as much marketing hype as engineering (and all indications are that Mercury is more of a sales organization than an engineering one) Then there is this business of power curves where power and torque vary with engine design for any given RPM. There are known occurrences of horsepower being overrated 20% or more by marketers so a spread of 40 HP DOWNWARD is certainly possible. In which event would be inclined to trust Yamaha's (or just about anyone's) veracity over Mercury. As you can tell, have gotten a pretty low opinion of Mercury Marine. Oh, and BTW, is the cam on your FrenkenMerc engine in sync with the other volumetric components (valve lift versus area, versus open (or close) time)? Have you checked breathing? Regards, HBH
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#6
11-17-2006, 10:09 AM
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Re: WOT speed on a '83 20' SF w/200
Phnx, last time i checked, 2 stroke engines don't have cams, or valves with measured lifts. As far as measured hp, most two strokes are under rated, the SAE measured hp ratings used by outboard manufactures allow 10% varriance in the claimed hp ratings. Most of the big V6 2 strokes, by all manufactures excede the ratings on the cowl. I have personally seen 225 Opti's make 245-250 hp on the dyno. I've also seen 225 fourstokes barely make the 10% under. There is no accross the board statement other than each engine has to make within 10 % of the cowl sticker when new. Right now Yamaha could sell their 150 four stroke as a 175( it makes 165-170 hp, but they decided not to because they got there but kicked when they introduced the 225 four stroke( it barely made 205hp).
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#8
11-17-2006, 05:07 PM
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Re: WOT speed on a '83 20' SF w/200
Spareparts beat me to it. PHNX - 150XR6 is a Merc 2.5L two stroke . . . Same block as the 2.5L 200hp.
Quote:
 But their old two stroke motors and inline motors are/were very good and strong. Yamaha - Yamaha's 2.6L motor is one of the most reliable engines, but the block was a masterfully engineered copy of the early OMC v6. 1983 lawsuit.
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#9
11-17-2006, 07:25 PM
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Re: WOT speed on a '83 20' SF w/200
they closed lake X
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#10
11-23-2006, 10:49 PM
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Re: WOT speed on a '83 20' SF w/200
Quote:
 http://www.f1boat.com/index.shtml
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