Another Impeller Question
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Another Impeller Question

  1. #1
    Member TV334's Avatar
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    Default Another Impeller Question

    I've got a bbc 496 that puts out about 780 hp and 700 ft lbs. I'm turning a AA impeller but all im getting out of it is about 4500 rpm. I'm new to this stuff so what should i be turning? Could i be overloading the pump, to big of a bite with the impeller, tuning issue? Thanks.

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    Senior Member YumaJet's Avatar
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    What kind of boat and bottom?
    What kind of pump and set up? Do you have a pressure guage for the pump? Many more questions need to be answered before anyone is able to give a decent answer. Its easy to say to cut down your impeller, but don't know if your boat is a ski boat with extra power or a boat made to run the track.
    boatless....

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    Seems to me that your rpms are really low but if you dynoed your engine where did you make the peak torque and h.p. if it was really high like say at 7500, then maybe that's the problem. Just a guess, but I would think that with 780 h.p. you ahould turn a AA near 6000 rpm.

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    Member TV334's Avatar
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    My boat is a 1988 18ft colorado custom v bottom hull. Its got a berekley 12jc with a dominator split bowl, snoot, and a place diverter. Its got a shoed intake with ride plate, the pump is not set back. I'm also running an impeller inducer plus an ulimate wear ring.

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    Senior Member YumaJet's Avatar
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    this has to be the most used pic around here.
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    boatless....

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    Member TV334's Avatar
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    my engine peaks torque at 5500 and hp at 6200.

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    Senior Member YumaJet's Avatar
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    Quote Originally Posted by TV334 View Post
    My boat is a 1988 18ft colorado custom v bottom hull. Its got a berekley 12jc with a dominator split bowl, snoot, and a place diverter. Its got a shoed intake with ride plate, the pump is not set back. I'm also running an impeller inducer plus an ulimate wear ring.
    Make sure the tach is working right. You have the power and pump to go above and beyond 6k rpm's. Might want to dbl check a few things.
    boatless....

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    Senior Member Oldsquirt's Avatar
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    Quote Originally Posted by TV334 View Post
    my engine peaks torque at 5500 and hp at 6200.
    If those numbers are from a dyno, please post the whole dyno sheet. Was it dyno'd where you live? You are at 4000+ feet which will put a bit of a hurt on actual output as compared to "corrected" numbers.

    What brand impeller? They aren't all the same in terms of the power required to turn them a given rpm.

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    Member TV334's Avatar
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    well im runnin a brand new tach and msd 6al. I dont have a way to post the whole dyno sheet wish i could. it was dynoed at 4900' and where i run it is about 4400'. Its a stainless hi-helix from duane at Hi tech.

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    Resident Ford Nut Sleeper CP's Avatar
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    Quote Originally Posted by TV334 View Post
    well im runnin a brand new tach and msd 6al. I dont have a way to post the whole dyno sheet wish i could. it was dynoed at 4900' and where i run it is about 4400'. Its a stainless hi-helix from duane at Hi tech.

    I'm guessing you posted the corrected dyno numbers, what were the observed numbers ?

    I'd think a 496 would have enough grunt to pull over 4,500 but the altitude just might the killing it. What's the intake on the engine ?

    Oh the AA HH will eat-up some trq,

    S CP

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    Senior Member hotbo's Avatar
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    start cutting the impeller.


    Hi-Helix will eat up some tq

    cut to a A cut and see how it likes it.then go from there
    WFLC


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    built by Scott Seastrom.

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    Senior Member Oldsquirt's Avatar
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    Quote Originally Posted by Sleeper CP View Post
    I'm guessing you posted the corrected dyno numbers, what were the observed numbers ?

    I'd think a 496 would have enough grunt to pull over 4,500 but the altitude just might the killing it. What's the intake on the engine ?

    Oh the AA HH will eat-up some trq,

    S CP
    Exactly what I was thinking.

    Did Duane ever put up any absorption data on the Hi-Helix impellers?

  15. #13
    Member TV334's Avatar
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    Those numbers were staight off the dyno sheet. Im running a profiler sniper ram with 2 8896 holley dominators.

  16. #14
    "Need For Speed" Gearhead's Avatar
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    TV....

    As per Sleeper and Old Squirt, do you have the UNCORRECTED Dyno numbers? If all your dyno guy offered you was the Corrected dyno sheet, you may want to call and ask for the "observed" or "uncorrected" dyno sheet. This will help a great deal in impeller sizing.

    If tested at 4900', the dyno correction factor back to sea level and STP is going to be fairly large.

    Have a good one.

    Gear
    Last edited by Gearhead; 11-13-2010 at 08:01 PM.

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