How do you pick an impeller
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How do you pick an impeller

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    Senior Member H20MOFO's Avatar
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    Default How do you pick an impeller

    O.K. I get the general gist ,aa=less r's per mph than a b cut ect..
    , but I mean if say your looking at a dyno sheet and an hp/rpm impeller sheet, would you want to your max on the impeller chart to corespond with your peak torque or hp or somewhere center or ?????? BTW does an impeller/hp chart exist for the new hi-helix yet?? hint hint hint
    Last edited by H20MOFO; 07-07-2008 at 08:38 PM.
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  3. #2
    Senior Member cyclone's Avatar
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    Quote Originally Posted by H20MOFO View Post
    O.K. I get the general gist ,aa=less r's per mph than a b cut ect..
    , but I mean if say your looking at a dyno sheet and an hp/rpm impeller sheet, would you want to your max on the impeller chart to corespond with your peak torque or hp or somewhere center or ?????? BTW does an impeller/hp chart exist for the new hi-helix yet?? hint hint hint
    1. what do you want to do with the boat? cruise efficiently, be real quick for short bursts of speed from a dead start, or go as fast as possible in a quarter mile? no matter what your answer to this question you should be able to pull skiers, wakeboarders etc even with a small diameter impeller if the pump is set up correctly so dont worry about that. Focus on what kinda performance characteristics you're looking for.

    2. if you've got a dyno sheet that will help. at what rpm does the engine make peak horsepower? is the curve pretty flat? what i mean by that is is the engine only making another 10hp every hundred rpm near the peak or is the increase larger or smaller than that?

    3. what kinda boat ya got? how heavy, how long?

    this info will help whoever you ask to pick an impeller cut figure things out for ya.

  4. #3
    jetboataholic HawaiianJet's Avatar
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    Quote Originally Posted by H20MOFO View Post
    O.K. I get the general gist ,aa=less r's per mph than a b cut ect..
    , but I mean if say your looking at a dyno sheet and an hp/rpm impeller sheet, would you want to your max on the impeller chart to corespond with your peak torque or hp or somewhere center or ?????? BTW does an impeller/hp chart exist for the new hi-helix yet?? hint hint hint
    I don't think that there is a chart for the hi-helix impeller, at least I haven't seen one posted here, and I can't find one on the HTP website. If you want to know something about them, or are having trouble selecting one. I would suggest giving Duane at HTP a call.
    HJ

    ***FOR SALE*** 1978 19' Full Stringer Hawaiian Molokai Jet Boat w/ Berkeley 12JC-AB and Chevy 440 Tall Deck ***FOR SALE***

    Quote Originally Posted by mako shark mark View Post
    Oh yeah, Forgot to mention that the hull is a special mixture of speedcote, herculiner and rain-x, all blended together- good for another 8 mph top end.

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    Senior Member H20MOFO's Avatar
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    Thanks Cyclone . I didn't want this thread to be me specific ... but I have a 21 daytona and my 427 isn't cutting it. And would like to do a 572 cid aaa impeller build ,n/a motor .... I dunno I just wondered for top end(not race) how would you pick an impeller ..how useful are those charts? I just want to do 80 plus and not kill my junk doing it.
    Last edited by H20MOFO; 07-07-2008 at 09:37 PM.
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    jetboataholic HawaiianJet's Avatar
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    Quote Originally Posted by H20MOFO View Post
    Thanks Cyclone . I didn't want this thread to be me specific ... but I have a 21 daytona and my 427 isn't cutting it. And would like to do a 572 cid aaa impeller build ,n/a motor .... I dunno I just wondered for top end(not race) how would you pick an impeller ..how useful are those charts? I just want to do 80 plus and not kill my junk doing it.
    What cut impeller are you using with the 427? I've got an AB cut paired up with my truck block, and I'm hoping it will be a good combination. I've been told that it should be.

    Good luck.

    HJ

    ***FOR SALE*** 1978 19' Full Stringer Hawaiian Molokai Jet Boat w/ Berkeley 12JC-AB and Chevy 440 Tall Deck ***FOR SALE***

    Quote Originally Posted by mako shark mark View Post
    Oh yeah, Forgot to mention that the hull is a special mixture of speedcote, herculiner and rain-x, all blended together- good for another 8 mph top end.

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    Senior Member H20MOFO's Avatar
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    I have an ab also. Mine's a short block 427
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    Senior Member cyclone's Avatar
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    Quote Originally Posted by H20MOFO View Post
    Thanks Cyclone . I didn't want this thread to be me specific ... but I have a 21 daytona and my 427 isn't cutting it. And would like to do a 572 cid aaa impeller build ,n/a motor .... I dunno I just wondered for top end(not race) how would you pick an impeller ..how useful are those charts? I just want to do 80 plus and not kill my junk doing it.
    its pretty much impossible to say which impeller will make the boat fastest with absolute certainty. You'll never know until the boat is in the water. With the info you have, a competent pump guy can use the charts to pick an impeller for the boat that runs near your engine' peak hp rpm at WOT, which would be a good place to start.

    If you find the rpm is way below your peak hp rpm and you're leaving a ton of power on the table then the shop can keep on trimming the impeller smaller to gain rpm and see if the speed increases until you reach that imaginary line of diminishing returns. Each trim will hurt the holeshot a small amount. But a really good pump guy can contour the front and rear of the impeller to bite hard even with a small diameter impeller.

  10. #8
    steelcomp was here
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    As long as the engine is producing more power than the impeller is absorbing, the impeller will continue to accelerate.
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    Senior Member H20MOFO's Avatar
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    Well put Steel... I guess I do shit backwards most people pick a impeller to go with there motor and I'm trying to design a motor around an impeller. lol
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  12. #10
    steelcomp was here
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    Quote Originally Posted by cyclone View Post
    its pretty much impossible to say which impeller will make the boat fastest with absolute certainty. You'll never know until the boat is in the water. With the info you have, a competent pump guy can use the charts to pick an impeller for the boat that runs near your engine' peak hp rpm at WOT, which would be a good place to start.

    If you find the rpm is way below your peak hp rpm and you're leaving a ton of power on the table then the shop can keep on trimming the impeller smaller to gain rpm and see if the speed increases until you reach that imaginary line of diminishing returns. Each trim will hurt the holeshot a small amount. But a really good pump guy can contour the front and rear of the impeller to bite hard even with a small diameter impeller.
    -OR- you can look at the power you're making and decide if you need to make some changes there. Sometimes more peak power isn't necessary...as cyclone said, if you find you're not pulling the impeller, maybe you can make some improvements to increase power at lower RPM and broaden your power curve...if that's your goal. If you;re not reaching peak power of teh engine it's because the power at a lower rpm is behind the power absorbtion curve of the impeller.
    If God is your co-pilot, change seats!
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  13. #11
    steelcomp was here
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    Quote Originally Posted by H20MOFO View Post
    Well put Steel... I guess I do shit backwards most people pick a impeller to go with there motor and I'm trying to design a motor around an impeller. lol
    You really have to look at them together as a combination. One of the reasons the NA guys have large cubic inches is it's way easier to build big, flat power at a reasonably low rpm. The smaller the cubic inches, the more difficult this becomes.
    If God is your co-pilot, change seats!
    Acts 2:38, the perfect answer to the perfect question.

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