HP or Torque for a jet???
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HP or Torque for a jet???

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    Senior Member Widetrack's Avatar
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    Default HP or Torque for a jet???

    What is best HP or Torque? Lets say I have a motor that makes 650 HP @ 5700 RPM and also 650 HP @ 6200 slight loss in HP between 57 - 62. But at 5700 torque is 640 and at 6200 it is 610 what RPM would I want the jet to turn for best performance?

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    jets love torque.................

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    Quote Originally Posted by AzEliminator View Post
    jets love torque.................
    heavy 1's do, light hulls like hp

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    21 Daytona Outlaw's Avatar
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    Quote Originally Posted by IMPATIENT 1 View Post
    heavy 1's do, light hulls like hp
    Does the engine/pump know what boat it is in?

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    Quote Originally Posted by Outlaw View Post
    Does the engine/pump know what boat it is in?
    lol, you're not drawing me into that arguement i ain't no newbie

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    Senior Member H20MOFO's Avatar
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    Both, if you build it they will come.
    Another Hot Boat refugee

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    Quote Originally Posted by IMPATIENT 1 View Post
    lol, you're not drawing me into that arguement i ain't no newbie
    .............

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    Senior Member Widetrack's Avatar
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    LMAO! You guys take the cake! but, it still leaves the question of RPM for the pump!

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    Quote Originally Posted by Widetrack View Post
    What is best HP or Torque? Lets say I have a motor that makes 650 HP @ 5700 RPM and also 650 HP @ 6200 slight loss in HP between 57 - 62. Unsure
    You have a hp dip between 5700 and 6200 ?

    What's your peak tq and what rpm ?
    What's your peak hp and what rpm ?

    Do you have a dyno sheet to show someone so they can help ?
    Can you give more details on the boat also ?

    BTW: I'm no jet boat guy, therefore I'm asking engine 'tune' questions and and other questions that may help others help you.

    Oh, and 6200 will sound faster than 5700. (joke)

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    Resident Ford Nut Sleeper CP's Avatar
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    Quote Originally Posted by Widetrack View Post
    What is best HP or Torque? Lets say I have a motor that makes 650 HP @ 5700 RPM and also 650 HP @ 6200 slight loss in HP between 57 - 62. But at 5700 torque is 640 and at 6200 it is 610 what RPM would I want the jet to turn for best performance?
    I love this question, it will not be easily answered. What are the observed HP #'s. I'm assuming the posted numbers are corrected ones.

    Off the top of my head I would guess an slightly worked Berkley A/B cut will put you at about 6,000 rpm's. I would start with that... Now if you go for a fully worked over race pump it could be as small as a B/C cut.

    You'll get about 15 different opinion's on this... Thanks for the entertainment.

    There is an Impeller chart posted here somewhere. If someone else doesn't post it I'll find it. Actually there are two charts.
    Edit:


    Also, do you have this engine or is this hypothetical ?

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    Last edited by Sleeper CP; 04-07-2008 at 04:13 PM.

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    B.A.M aka "Black Azz Mike 396_Ways_To_Spit's Avatar
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    This is one of the most debated topics I have been viewing since 2000

    This thread should get pretty damn good...................
    G H E T T O F O E L I F E
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    Quote Originally Posted by Widetrack View Post
    What is best HP or Torque? Lets say I have a motor that makes 650 HP @ 5700 RPM and also 650 HP @ 6200 slight loss in HP between 57 - 62. But at 5700 torque is 640 and at 6200 it is 610 what RPM would I want the jet to turn for best performance?
    Depends.

    Depends on what RPM you want to twist the engine to.
    Depends on what impeller cut you want to run.
    Depends on what youy want to use the boat for.
    Depends on how you want to define "performance", BY INTENDED USAGE.

    "Performance" for a 1/4 mile drag jet is nowhere near the same as "performance" for a lake boat that pulls people on tubes/skiis all day and carries 5 people to fireworks shows 5 miles down-lake in the evening and then back.

    Generally, larger impellers reduce RPM (thus engine wear and fuel consumption), increase acceleration (holeshot) and increase pulling ability (skiis/tubes).

    Conversely, Generally, smaller impellers make slightly more top speed, at a loss of acceleration and pulling ability, and require higher RPM.

    Torque is the only thing an engine generates anyhow, "twisting force by the crankshaft" is TORQUE.

    All Horsepower is is a mathematical calculation of torque generated over time.
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    Quote Originally Posted by 396_Ways_To_Spit View Post
    This is one of the most debated topics I have been viewing since 2000

    This thread should get pretty damn good...................
    Yea, it is 396, and I will most likely be lurking for the rest of the fight.
    "As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron."
    H.L. Mencken

    OBAMA: Some people deserve this.
    The rest of us are being dragged along kicking and screaming.

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    Sit N' Spin Jetaholic's Avatar
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    Quote Originally Posted by Outlaw View Post
    Does the engine/pump know what boat it is in?
    To answer this...no they don't. The engine just spins the pump, the pump allows the engine to swing up to a certain max RPM depending on how well the pump loads, engine HP curve, etc etc. X amount of thrust is made...and that's where thrust/weight ratio comes in.

    Honestly..the whole "heavy boats like torque, lighter boats like HP"...if you have a motor with enough torque to shoot a heavier boat out of the hole like a rocket and you put that same motor with the same pump in a lighter boat, I would think it would do even better in the lighter boat due to less weight.

    But the one point nobody can argue with...jet boats definitely prefer Chevy over Ford

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