Yet another inlet PSI question
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Yet another inlet PSI question

  1. #1
    Impeachment! 75 TX's Avatar
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    Default Yet another inlet PSI question

    I drilled and tapped my suction for inlet psi @ 9oclock. It reads between 32-37psi, depending on shoe/depth, and nozzle size. 35-37 with my best (to date) setup in the boat.
    A few weeks later I stopped by Jack's shop and he advised me that a better place to take a reading from would be up higher, at about 10-11oclock, as the top of the impeller is harder to load.
    So yesterday I took the boat out for the 1st time since adding the 2nd tap. 1st couple passes the low tap read 35psi. I then switched to the high tap and saw consistent readings of 36-37psi, though I'd have thought it'd be less than the low tap.
    Anyone have any ideas why the high tap might see more psi than the low?

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    Senior Member zacho!'s Avatar
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    Good loader? Didnt you have one custom made?

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    Senior Member bp298's Avatar
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    on the wall of the suction piece, the closer to the impeller, the higher the pressure.

    basically. you are scooping a column of water at the same speed the boat is travelling. at the intake opening, pressure is close to atmospheric, but the velocity up into the suction piece is high (i.e., if you were removing water as fast as it entered, suction pressure would be 0). the closer it gets to the impeller, the more the water molecules slow down. since the velocity energy must be conserved, velocity energy converts to pressure energy.... basically...

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    1977 Custom Sprint Jet wickedsanger's Avatar
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    Quote Originally Posted by bp298 View Post
    on the wall of the suction piece, the closer to the impeller, the higher the pressure.

    basically. you are scooping a column of water at the same speed the boat is travelling. at the intake opening, pressure is close to atmospheric, but the velocity up into the suction piece is high (i.e., if you were removing water as fast as it entered, suction pressure would be 0). the closer it gets to the impeller, the more the water molecules slow down. since the velocity energy must be conserved, velocity energy converts to pressure energy.... basically...
    WOW!!!! Thats a mouth full!!!!!!!
    Wickedsanger... Gettin it done with a Small Block!!!!

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    Super Moderator HammerDown's Avatar
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    There's someone on this forum that told me, when he gets done doing his magic to the pump >>> 8-lbs is plenty and no more is needed.
    My lips are sealed to whom that person is
    <img src=http://www.performanceboats.com/gallery/data/500/medium/06-30-11_1234.jpg border=0 alt= />

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    Super Moderator HammerDown's Avatar
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    Quote Originally Posted by bp298 View Post
    on the wall of the suction piece, the closer to the impeller, the higher the pressure.

    basically. you are scooping a column of water at the same speed the boat is travelling. at the intake opening, pressure is close to atmospheric, but the velocity up into the suction piece is high (i.e., if you were removing water as fast as it entered, suction pressure would be 0). the closer it gets to the impeller, the more the water molecules slow down. since the velocity energy must be conserved, velocity energy converts to pressure energy.... basically...
    Where's MikeT when I need him
    <img src=http://www.performanceboats.com/gallery/data/500/medium/06-30-11_1234.jpg border=0 alt= />

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    Impeachment! 75 TX's Avatar
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    Quote Originally Posted by zacho! View Post
    Good loader? Didnt you have one custom made?
    Yup. A real nice MPD open center one.
    What kinda inlet pressures are you seein' high and low?

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    Senior Member cyclone's Avatar
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    Quote Originally Posted by HammerDown View Post
    There's someone on this forum that told me, when he gets done doing his magic to the pump >>> 8-lbs is plenty and no more is needed.
    My lips are sealed to whom that person is
    Timinator?

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    Super Moderator HammerDown's Avatar
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    Quote Originally Posted by cyclone View Post
    Timinator?
    I'll never tell...
    <img src=http://www.performanceboats.com/gallery/data/500/medium/06-30-11_1234.jpg border=0 alt= />

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    Senior Member zacho!'s Avatar
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    Quote Originally Posted by 75 TX View Post
    Yup. A real nice MPD open center one.
    What kinda inlet pressures are you seein' high and low?
    I run a "hand me down" loader. Flat shoe, around 20#'s high and 30#'s low, v-hull. I think it runs incredible, but I'm sure a pro would tell me different. One of the really fast racers here in tucson said I need a center blocker for more lift ... at some point Ill be able to work with JM, who built the said racer's pump.

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    Senior Member cyclone's Avatar
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    Quote Originally Posted by HammerDown View Post
    I'll never tell...
    he's stated as much before. Can't say I agree with it but would like to see some sort of test to prove it.

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    Senior Member bp298's Avatar
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    Quote Originally Posted by wickedsanger View Post
    WOW!!!! Thats a mouth full!!!!!!!
    just a basic description. the long version would be a mouthful. it is what it is.

    Quote Originally Posted by HammerDown View Post
    My lips are sealed to whom that person is
    doesn't matter, everyone knows who it is. unfortunately, this has nothing to do with the op's question. also unfortunately, "your guy" has never had a boat on a track to demonstrate it.

    Quote Originally Posted by cyclone
    he's stated as much before. Can't say I agree with it but would like to see some sort of test to prove it.
    it would be very interesting to see an actual data file with 3-4 suction pressure taps, top and bottom, along with a couple bowl pressure taps, and see what the trends are when you're trying to maintain 8 psig suction pressure at 110-130.

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    B1 Racing cs19's Avatar
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    Quote Originally Posted by 75 TX View Post
    Anyone have any ideas why the high tap might see more psi than the low?

    Its tottally normal that the high inlet is higher. In fact your low and high are pretty equal, I'd say your doing real well with your setup.

  16. #14
    Senior Member cyclone's Avatar
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    Quote Originally Posted by bp298 View Post
    just a basic description. the long version would be a mouthful. it is what it is.



    doesn't matter, everyone knows who it is. unfortunately, this has nothing to do with the op's question. also unfortunately, "your guy" has never had a boat on a track to demonstrate it.



    it would be very interesting to see an actual data file with 3-4 suction pressure taps, top and bottom, along with a couple bowl pressure taps, and see what the trends are when you're trying to maintain 8 psig suction pressure at 110-130.
    I'd like to see a boat that goes 100+ with only 8psi inlet pressure. that would be an accomplishment.

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