Just Curious....
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Just Curious....

  1. #1
    Senior Member bajadad's Avatar
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    Default Just Curious....

    Has anybody ever put a shorty Powerglide, or some kind of high gear set-up in a Jet Boat? I seen turbo 400's in an outdrive set-up, they drove buy at like 90mph 2k rpms......I think it would look like crap, but there's gotta be someone out there thats done it.

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    Thrust Whisperer Doc Nozzle's Avatar
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    X2 on curious about the same thing. Add to this question the possibility someone used one of those bolt-on RV overdrive trannies.

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    Resident Ford Nut Sleeper CP's Avatar
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    the impeller is a water dyno, you have to create trq to turn it; even a "D" cut impeller at a 4,000 will take some power and not move allot of water. You have to pump water (GPM) to get a jet pump to move the boat. The tranny at low rpm just wont work ( so I've been told)

    I have thought about it a few times, would love to see what would happen. Best quess is you need a big stroker that makes 700 hp at 4,500 and 1,000 or something like that at 6,500 and you overdrive it. The problem is the load at 4,500. you would have to make that power at part throttle. You wouldn't want to be running up river WOT sucking tons of fuel to move your boat at 60 mph. The CP runs 50+/- at 4,000 in the primaries. The secondaries are just opening at 4,000.

    Looking at an impeller chart you can see what the load on the engine would be like. Ignore the writing on the chart.



    Sleeper CP
    Last edited by Sleeper CP; 06-29-2009 at 02:57 PM.

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    Senior Member bajadad's Avatar
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    Something like a Gear Venders overdrive. It would work, just like a car you need a bunch of hp to push hi gear. I think with 600 to 700 hp it could done. Gear vender is inline setup.

    A Bugatti Veyron will do 256 mph, it takes 250hp to go 150mph, and another 750 to go from 150 to 256mph. The car has 1004hp.

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    Resident Ford Nut Sleeper CP's Avatar
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    Quote Originally Posted by bajadad View Post
    Something like a Gear Venders overdrive. It would work, just like a car you need a bunch of hp to push hi gear. I think with 600 to 700 hp it could done. Gear vender is inline setup.

    .
    You want to use 700 hp at what rpm. The juice may not be worth the squeeze. IE running under a hard load for 10 miles up/down river at WOT, how much fuel will you use doing that ?

    I'd sure like to try a few set-ups. Something tells me you'd be better off with a twin pump boat spinning two smaller impellers at a higher RPM.

    S CP

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    Senior Member bajadad's Avatar
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    Just talked to Gear Venders, they had a customer do this to a jet boat 22% overdrive. Nothin crazy hp wise, i'm still diggin the sales guy that set it up is gonna give me a call back, try to dig up some pics.

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    Senior Member old rigger's Avatar
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    We placed a "Z-drive" between the engine and the pump in the 80's at Rogers in a 19TR. Still only a one gear direct drive, but like a V-drive you could play with the gear ratio.

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    I do all my own stunts. white tortilla's Avatar
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    my dad put a lenco trans on the back of a tpr stealth, to try to get higher rpms, but the loss of hp to turn the tranny made it more efficent to run it w/o a tranny at lower rpms, without the tranny robbing the power

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    Quote Originally Posted by bajadad View Post
    Just talked to Gear Venders, they had a customer do this to a jet boat 22% overdrive. Nothin crazy hp wise, i'm still diggin the sales guy that set it up is gonna give me a call back, try to dig up some pics.
    I tinbk this is the 3rd time I've seen this topic since my HotBoat days starting in June of '07.

    Here's a lower rpm chart:



    At 22% an engine spinning 4,000 would spin the pump 4,900. As stated above there would be some power losses turning through the tranny.

    S CP

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    Senior Member bajadad's Avatar
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    I agree, but you got to admit that hearing a jet boat shift would be kinda sexy....

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    Senior Member cave's Avatar
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    we talk about this at every get together. Some kind of Lenco inners for a 2 speed or a Hi / Low. In line with the drive line.

    Like I said, we get this going often. If it could be done a Drag Boater would have already have done it. A sprag of some type to slide forward & reverse for the gear change. Dam that would be bad a$$..

    Imagine the ET's
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  14. #12
    Sit N' Spin Jetaholic's Avatar
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    Take a look at what a transmission does in a car. From a dead stop, the engine hits a certain RPM when you stab the throttle. As the tires start turning, the load on the engine drops, allowing the RPMs to increase.

    Once the engine's vacuum rises back up as the engine load decreases, the transmission shifts to the next higher gear, reloading the engine, which drops the RPMs back down until the wheels pick up more speed and unload the engine again.

    Props kinda do the same thing. As they move through the water, the front of them will unload, allowing the RPM to climb as the engine load drops.

    The whole purpose of the transmission is to continuously re-apply a load to the engine that keeps the engine in its power band by shifting to higher gears as the vehicle accelerates and decreases that load.

    Jet drives do this by default. The faster you spin them, the more load they apply to the engine. The load the engine sees is provided by the amount of water the impeller is trying to squeeze through the pump. The higher the RPM, the more water squeezed, and therefore the higher the load applied to the engine. This load is completely independant of the boat's movement through the water. This is why when you dump it to the floor, the RPMs immediately hit the max RPM the pump will allow it to no matter what your forward speed is. If the impeller size is ideally matched by the book to the engine, the impeller will allow the engine to spin up to its peak horsepower RPM and no higher than that. Jets act very much like a high stall torque converter. You stab the throttle to the floor, the RPMs immediately increase to the max that the pump will ever allow it to spin, and stay there until you back out of the throttle regardless of the forward speed of the boat. In any throttle position, if the throttle is held in one position, the RPMs stay put as the boat accelerates because a jet drive is a constant load regardless of forward speed. In all actuality, the pump and engine have no idea that they're moving anything, unlike a car or a propeller driven boat. As was stated before, a jet drive can be related to a high stall torque converter, a dyno or waterbrake.

    For the above mentioned reasons, IMHO a transmission would have no use in a jet boat.
    Last edited by Jetaholic; 06-29-2009 at 05:11 PM.



    Quote Originally Posted by HammerDown
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    Sit N' Spin Jetaholic's Avatar
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    Always did wonder if there'd be any real reason to put a clutch in a jet though



    Quote Originally Posted by HammerDown
    Kendall L-427 Super Blu...extreme-pressure (ep) lithium complex keeps my thrusting balls happy
    Quote Originally Posted by back2k5 View Post
    Well I am putting in a nice stereo system in the Carrera...maybe Ill put on some rap and turn the scoop sideways

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    21 Daytona Outlaw's Avatar
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    Quote Originally Posted by bajadad View Post
    I agree, but you got to admit that hearing a jet boat shift would be kinda sexy....
    How many jet boaters are willing to give up 16" of leg room
    to add a gear vendor unit, I've installed several GV's in pickups
    and they are simple and work great, just dont know about in a jet boat.
    I would like to see one done at least for testing.
    #55

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