different rpm at WOT

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GMAC 76
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different rpm at WOT

Post by GMAC 76 »

why is there so much difference in WOT engine rpm from the trailer to the lake i just put a new prop on a 540 dialed in the pitch to turn 2800 on the trailer left everything the same took it to the lake and the engine turned up to nearly 2950 can someone tell me what causes this???

arcticman
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Re: different rpm at WOT

Post by arcticman »

cause yur haulin asss :lol: :lol: :lol:

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yobee
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Re: different rpm at WOT

Post by yobee »

Best way I can explain for it to make sense is that on the trailer your prop has to suck air, moving on the water it's being fed air and it gets to free up a little bit. Make sense? It is common to gain rpm like that.
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GMAC 76
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Re: different rpm at WOT

Post by GMAC 76 »

u r right sir!!! i kinda like that 2950 but why does it happen?

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plumcrazy
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Re: different rpm at WOT

Post by plumcrazy »

your moving threw the air/ on the trailer your just moving air/ most boats will gain a hun or too on the water

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Re: different rpm at WOT

Post by PJC »

sometimes if you have a large prop that catches some air it can actually turn slowly while pulling it down the road

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Champ18ft
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Re: different rpm at WOT

Post by Champ18ft »

It's all Rocket Science. Some things just can't be explained.
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Tony480
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Re: different rpm at WOT

Post by Tony480 »

PJC wrote:sometimes if you have a large prop that catches some air it can actually turn slowly while pulling it down the road
NO THAT IS CALLED HAVING A WORE OUT MOTOR WITH NO COMPRESSION. :lol:

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Re: different rpm at WOT

Post by pax1ton »

Its called static thrust when your on the trailer (The measured thrust produced when movement is prevented) heres your rocket science on it http://www.mh-aerotools.de/airfoils/prpstati.htm

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Re: different rpm at WOT

Post by johnnybeeegood »

eighth wonder

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watersports7
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Re: different rpm at WOT

Post by watersports7 »

Forced Air Induction :wink:
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harley
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Re: different rpm at WOT

Post by harley »

yobee wrote:Best way I can explain for it to make sense is that on the trailer your prop has to suck air, moving on the water it's being fed air and it gets to free up a little bit. Make sense? It is common to gain rpm like that.
That makes good sence to ME also yobee... my last 3 boats all had different rpm's ... from - trailer to water, they all gained at lesat - 150 = 190 more rpm ... 8)
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watersports7
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Re: different rpm at WOT

Post by watersports7 »

Champ18ft wrote:It's all Rocket Science. Some things just can't be explained.
:lol: :lol: :lol:
12' Predator / Lycoming 4 Cylinder / Old Skool 68x38 Stick Prop
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Southern Style
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Re: different rpm at WOT

Post by Southern Style »

Seems that I heard something bout "Static" RPM's... This is where your rpm's are on a trailer at 2850 because it has to work to push the air thru with no help... When on the river, you actually have air helping it by movement causing you to see 2950 to 3000 rpm's... Just a little assistance thats all..........
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watersports7
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Re: different rpm at WOT

Post by watersports7 »

waterthunder had a good explanation of this a while back, its like hanging your hand/arm out of your trucks window at speed, (FEEL THE FORCED AIR INDUCTION) will try to find the post, maybe Dave will chime in...
12' Predator / Lycoming 4 Cylinder / Old Skool 68x38 Stick Prop
Perfectly said by Lycoming: Some engines purr like kittens. These roar!

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