would this work.
+ Reply to Thread
Results 1 to 13 of 13

Thread:
would this work.

  1. #1
    Senior Member
    Join Date
    Apr 2008
    Location
    valley springs, ca
    Posts
    1,244

    Default would this work.

    i have a spectra 20 jet. im considering setting the pump back on it. when doing so would i be able to move the engine forward a little to but a 2 speed shortie in there. i have never seen it done and you think it would work

  2. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  3. #2
    Senior Member bajadad's Avatar
    Join Date
    Mar 2009
    Location
    Yucaipa Ca
    Posts
    653

    Default

    I brought this up, and got shot down. I'm interested, are you useing a Gear Vender unit? If not what are you useing? Keep me informed.

  4. #3

    Join Date
    Aug 2009
    Posts
    85

    Default

    I was thinking along these lines at one time. I was going to go with an old 3 speed manual. basicaly because its shorter and there is less parasitic loss from a torque converter. The problem is you dont get 1 to 1 untill 3rd. This is not what i was trying to accomplish. I wanted to keep the motor rpms lower while keeping the pump rpms up.

  5. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  6. #4
    Sit N' Spin Jetaholic's Avatar
    Join Date
    Dec 2007
    Location
    Droppin' the kids off at the pool
    Posts
    1,423

    Default

    The purpose of a transmission in a car is to reapply a load to the engine that places the engine back in its power band after the RPM of the spinning wheels has increased to a point that drops the load on the engine enough to cause it to overspin its powerband. This doesn't happen in a jet boat. Engine load in a jet boat increases with RPM and is not affected by the boat's acceleration, while engine load in a car decreases with acceleration.

    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.

    Even if you were to use one to overdrive the pump at cruise to lower RPMs, in reality you would be forcing the engine to do more work at a lower RPM than you would be with a 1:1 drive. Example, let's say the pump is spinning at 3500 RPM, but the overdrive in the trans keeps the motor at 2000. Now it's having to drive not only the trans, but the pump as well. This means the engine is seeing a slightly higher load than it would normally see at 3500 RPM with a 1:1 drive, but it's seeing this load at a lower RPM. This would drastically drop fuel economy.

    For the above mentioned reasons, IMHO a transmission has no place in a lake cruiser jet boat application.
    Last edited by Jetaholic; 08-16-2009 at 11:12 PM.



    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

  7. #5

    Join Date
    Aug 2009
    Posts
    85

    Default

    So if you need 450 to turn 5200, what would you turn if say 1000hp

  8. #6
    Sit N' Spin Jetaholic's Avatar
    Join Date
    Dec 2007
    Location
    Droppin' the kids off at the pool
    Posts
    1,423

    Default

    Quote Originally Posted by millwrightlong View Post
    So if you need 450 to turn 5200, what would you turn if say 1000hp
    According to Berkeley's impeller power curve chart, an A cut impeller requires 450hp to spin 5200RPM.

    According to the extended power curve chart, 1000hp on an A would spin 6800 RPM.

    Also by looking at the charts, you can see that engine load increases with pump RPM. When you hold the throttle at one particular RPM setting, then stab the throttle to another RPM setting, the RPMs INSTANTLY swing up to the next RPM setting regardless of boat speed. The RPMs also hold constant as the boat accelerates, which proves that boat speed/acceleration does not affect engine load. However, the engine sees a higher load at the higher RPM setting than it does at the lower RPM setting. This is because a jet drive is a constant load that is RPM dependant. As RPMs increase, water flow through the pump also increases, which increases engine load. If engine load was affected by the boat's speed/acceleration, when you stab the throttle the speed of the boat would limit how far the RPMs increased when the throttle was stabbed, then would increase as the boat acceleratedm but this does not happen.



    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Impeller_Chart_ExtendedA.jpg 
Views:	406 
Size:	78.5 KB 
ID:	51059   Click image for larger version. 

Name:	pwr-curve-lg.jpg 
Views:	1173 
Size:	64.9 KB 
ID:	51060  
    Last edited by Jetaholic; 08-16-2009 at 10:47 PM.



    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

  9. #7
    Resident Ford Nut Sleeper CP's Avatar
    Join Date
    Dec 2007
    Location
    San Diego County
    Posts
    10,072

    Default

    Quote Originally Posted by Jetaholic View Post

    Even if you were to use one to overdrive the pump at cruise to lower RPMs, in reality you would be forcing the engine to do more work at a lower RPM than you would be with a 1:1 drive. Example, let's say the pump is spinning at 3500 RPM, but the overdrive in the trans keeps the motor at 2000. Now it's having to drive not only the trans, but the pump as well. This means the engine is seeing a slightly higher load than it would normally see at 3500 RPM with a 1:1 drive, but it's seeing this load at a lower RPM. This would drastically drop fuel economy.
    For the above mentioned reasons, IMHO a transmission has no place in a jet boat application.

    I'd think so, the engine would have to work harder ( bigger load) at a lower RPM. I would think this would eat more fuel. You really need to look at this on a lower RPM scale. I'd like to see it tried and be proven wrong:


    My stroker Windsor would have more than enough reserve power to do it in a small to mid-size boat. I'd like to see it tried, maybe it was and it was a disaster so it hasn't been done again.




    Sleeper CP
    Last edited by Sleeper CP; 08-16-2009 at 11:02 PM.

    "Dark Sarcasm"
    Going fast is only half the fun ... what you make go
    fast is the other half.
    " A Government big enough to give you everything you want is big enough to take away everything you have"

  10. #8
    Crazy Eights Brad @ SCJB's Avatar
    Join Date
    Dec 2007
    Location
    Las Vegas, NV
    Posts
    1,476

    Default

    there he goes again.....

  11. #9
    Sit N' Spin Jetaholic's Avatar
    Join Date
    Dec 2007
    Location
    Droppin' the kids off at the pool
    Posts
    1,423

    Default

    Quote Originally Posted by Sleeper CP View Post
    I'd think so, the engine would have to work harder ( bigger load) at a lower RPM. I would think this would eat more fuel. You really need to look at this on a lower RPM scale. I'd like to see it tried and be proven wrong:


    My stroker Windsor would have more than enough reserve power to do it in a small to mid-size boat. I'd like to see it tried, maybe it was and it was a disaster so it hasn't been done again.




    Sleeper CP
    Since fuel economy goes out the window in a race situation, I could see how an overdrive MIGHT get you off the line like a rocket, then downshift to 1:1. But using one in a cruiser would be pointless IMO. But RPMs in a jet increase so quickly it makes me wonder if it would spin the pump up to quickly with an overdrive and cause it to slip out of the hole.

    The point I was trying to make was that some people expect a transmission in a jet boat to perform like it would in an automotive application or a prop drive app. However, since load is INCREASING with RPM rather than DECREASING with forward speed like it would in a car or prop drive, as RPM increased you would have to downshift until you got to a 1:1 drive, unless your motor makes max hp at an RPM much higher than it could spin the impeller with a 1:1 drive. But since the pump doesn't pose much of a load on the engine until above 4000, what would be the benefit of making the engine produce the same horsepower it would produce at 3500 at a lower RPM than that?
    Last edited by Jetaholic; 08-16-2009 at 11:34 PM.



    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

  12. #10
    Senior Member Futs's Avatar
    Join Date
    Dec 2007
    Location
    Orange CA, Big River
    Posts
    4,549

    Default

    Quote Originally Posted by Brad @ SCJB View Post
    there he goes again.....
    It's ok they are all new...

  13. #11
    Senior Member LuckyDaze's Avatar
    Join Date
    Apr 2008
    Location
    Tacoma Wa
    Posts
    1,409

    Default

    Miller used a z drive system in the boat lo rider, not certain if they geared it to over drive the pump though.

  14. #12
    Senior Member Futs's Avatar
    Join Date
    Dec 2007
    Location
    Orange CA, Big River
    Posts
    4,549

    Default

    Quote Originally Posted by LuckyDaze View Post
    Miller used a z drive system in the boat lo rider, not certain if they geared it to over drive the pump though.
    You would be correct. But they are talking about being able to shift gears. It was tries in the 70's, but nothing really came about of it.But with the technoligy of today, anythings possiable.

  15. #13
    www.highflowdynamics.com LakesOnly's Avatar
    Join Date
    Dec 2007
    Location
    San Francisco Bay Area
    Posts
    1,160

    Cool

    Quote Originally Posted by sangerfan76 View Post
    i have a spectra 20 jet. im considering setting the pump back on it. when doing so would i be able to move the engine forward a little to but a 2 speed shortie in there. i have never seen it done and you think it would work
    It's not a prop boat, sangerfan76, it won't work the way you're hoping it will. Also, I'll bet that moving the motor forward is more likely to hurt top speed than help it.

    If you want your boat to be faster, you would need more compression & cam in your current engine, or a stroker shortblock, etc. Glad you're enjoying the jet boat and into getting more power, but even from a gearhead point of view I'm not so sure the trans thing is a good idea. Also, don't lose sight of the original intention of your cruiser in the first place, and build the big engine (and maybe a trans) for the prop boats that you have in the works instead.

    If you really just want more power out of wifey's current ride, give me a call and we'll make it happen.

    LO
    High Flow Dynamics
    Performance Components for the 429/460 Engine Family


    This post © Copyright 2007-2017 Paul Kane. No copying, linking, printing or otherwise without express written permission.

+ Reply to Thread

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Please select your insurance company (Optional)

Log-in


Digg This Thread

Posting Permissions

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
  •  
 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95