1999 Yamaha 3.1L OX66 200HP Prop Suggestions

rjcamel2355

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What would you guys suggest to run on this engine? Currently turns a 25P 3 Blade yamaha prop, but I think it could handle a bigger one. Running on a 20'7" Skeeter. The tach says somewhere around 6500RPMS (but I am almost CERTAIN that isn't right).

There is a prop shop nearby, would it be worth it to have the pitch changed to a 26/27?
 

Sea Rider

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Firstly check if current tach is in good working order before repitching...What's the min-max wot rpm range factory stated for that motor ?

Happy Boating
 

rjcamel2355

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5600-5800 I believe but ill check. I've read they have a 6200rpm rev limiter is why I am questioning the 6500rpm reading. Do you happen to know what would cause a false tach reading on these engines?
 

Sea Rider

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Probably tach is way off, uncalibrated, check contacts, ground to be clean, was it properly set, was tach working right before having rpm excess ? See if can borrow a shop tach and test along current one. Or buy an induction tach model :

https://www.hardlineproducts.com/pro...o-8-cylinders/

Check Iboats, Amazon

Happy Boating
 
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rjcamel2355

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Tested it all out over the weekend, it turns 6000RPMS @ WOT, full tank of fuel, full load, 3 people, @66MPH, Operating range on the motor is 4500-5500 with the limiter at 6100, so could I safely go from the 25M stock prop, to a 26? it has plenty of holeshot and power, I'd just like to see a bit more speed (it can go up a LOT on the jackplate, but I didn't want to start messing with that quite yet).
 

Sea Rider

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Is that a inboard or outboard engine ? By jackplate you mean can rise or lower engine on transom ? If so, would check ideal OB/Transom height and once matched go for a prop maximization.

The issue is that's impossible to know how much wot rpm will loose going + one pitch, say to a 26. Could reduce 200 or way more, will need to discover that on a wot run as usually loaded. If not mistake prop shops can repitch up to 2 full sizes along half sizes if needed.

Happy Boating
 

rjcamel2355

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It's an outboard, V6 engine. Yessir, it has a manual jackplate that I can raise/lower the engine on the transom. I believe you're correct on being able to raise/lower pitch, they can also add rake/cup and all those fancy terms. I'm well above the 4500-5500RPM range, and on the border of the RPM limit, I just would hate to repitch my current prop, and have to turn around and have it taken back to a 25 if it didn't quite do what I was expecting... If that makes any sense.
 

Sea Rider

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Can you post an OB pic shot sideways where both horizontal plates are visible. How much would a repitch from 25 to 26 cost ? If OB already revs at 6500 rpm, do you plan lowering it as currently loaded to say 6000 or max 5500 wot rpm stated factory range ?

The plenty, probably astonishing more hole shot power combo is experincing is due to the fact that OB is over revving. Anyway with a 26 pitch will achieve less wot revs compared to a 25 while currently loaded...

For boating perfection you need to spend some cash, it's done once, after that will boat happily forever.

Happy Boating
 

rjcamel2355

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I'll get a picture of the motor and location on the boat this afternoon, hopefully it will shed some light on the situation.
Currently at WOT loaded, with 3 people in the boat it turns 6000 RPMS
Factory RPM range is 4500-5500
RPM limiter is at 6100RPMS
Current prop is a 25 pitch Yamaha 25M

Cost to have the prop worked is $100

I feel like it is about right on the transom, the previous owner said he attempted to adjust it a few times, but if he went up anymore it would begin to Chinewalk, I don't mind chinewalk at all, but I just want to be propped appropriately before I start making too many adjustments.
 

Sea Rider

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On first post you said that OB revved at 6500 rpm, now at 6 K as currently loaded with 3 up. Was 6.5 K revs achieved while same loaded as in previous post ? If rev limiter didn't kicked in at 6.5 wot revs, tach must be way off, don't know if rev limiter system goes bad over time or stops working at all ?

Once pic/s are posted will give some OB/transom height parameters to check while cruising before messing with + prop pitches.

Happy Boating
 

rjcamel2355

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Apr 22, 2015
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I misread the tach, when me and the previous owner went out in the boat, I glanced over at the tach and from my position it looked like it read 6500RPMS, I took it out this weekend (first time being on the water, in the drivers seat) and the tach was at 6000RPMS, that was WOT trimmed up, giving it all it had.

Water pressure gauge stayed between 18 and 20PSI, so I believe there is a little room to raise the motor, but I will definitely get some pictures as soon as I make it home this afternoon.

I'm sorry about that....

Rev limiter is at 6100 (according to the engine specs), and I haven't yet hit that, so I'm inclined to believe the tach is working properly @6000RPMS,

Thank you Sea Rider, I really appreciate you taking the time to help me out on this.
 

Sea Rider

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Have added a new pic of a Yam 150 HP, lower tail should be same shape.

Parameters :

-Test on flat calm, no wind water cond, preferably at early morning.
-Distribute weight evenly on deck with 3 up.
-One heavy boater up front.
-Driver.
-One light boater aft (transom side)
-Go for a 3/4 throttle or full wot run, when on plane set trim to 90? for combo to ride parallel to water level.
-Once there both lower horizontal plates will ride parallel to water flow too.
-Determine at which 1-2-3 lower tail height is middlle water flow passing at speed ?

Yam 200.JPG

For that will need boater sitting aft to pull head out while riding at a straight water course to check that out, could tell a friend with other boat to ride close to back of motor to check or fly a drone with camera to check that too, will need a super fast one LOL!!. Report your findings....

Engine/Transom Height Optimization along Prop Maximization is the way to go to take the max power & fun out of that nice combo.

Happy Boating
 
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