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Question for you guys

  1. #1
    Senior Member cave's Avatar
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    Default Question for you guys

    Summary, I spent the last 4 months rebuilding the engine. I added a 6/71 blower. With the intake & carbs, I would say the two weigh somewhere around 100lbs. Before the Blower. At 4900 rpm the boat ran a solid 73 + on GPS. Now with the blower, 4lbs of boost (8% under driven) 5500 rpm the boat runs 69.9 on gps.

    If I now picked up 100 extra pounds but increased the rpms by 6k should I be at least equal to what I was running?

    I did change out the cam for a blower friendly cam with less duration.

    If I increased the rpms shouldn't I have a bit more speed or is that 100 lbs extra that much more a negative than a positive???

    I have a thread in the West Coast South that show the build. Oh and the videos that I show with me running the engine are with the PTO disconnected.
    Takin it home

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  3. #2
    mo balls than $cents$ IMPATIENT 1's Avatar
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    you'd expect a mph loss with a 120lb passenger if you're runnin the exact same longblock, but with a blower now, you may be only making the same amount of hp 4lbs isn't much, and you've gotta overcome parasitic loss from turning a the blower, then its weight. try 1 to 1 on the pulleys.

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  4. #3
    Senior Member H20MOFO's Avatar
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    Yeh, but he picked up 600 r's if that won't carry around a person or 2??? So you didn't change impellers or anything??
    Another Hot Boat refugee

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  6. #4
    Senior Member Brendellajet's Avatar
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    Hows the pump? If you picked up R's and went slower Something aint right. 100 lbs is a hot chick, shouldn't slow the boat down that much.

  7. #5
    i got skiillllzzzz.... fast76rogers's Avatar
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    what loader grate do you have?i changed from a hardin "ss" series to the "xs" and picked up 12mph.with your hp change you might have to load your pump different. just my guess.

  8. #6
    Senior Member cave's Avatar
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    The only change was the Blower addition and new cam.
    Same MPD Loader.
    Takin it home

  9. #7
    Senior Member moneysucker's Avatar
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    something aint right there. With additional RPMs you should be picking up speed. I could not even tell you what the change was when I added a blower because I had to mess with EVERYTHING at the same time.
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  10. #8
    Senior Member milkmoney's Avatar
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    so if i lose the thirty pounds of fat i will be the fastest on the river, sorry had a few, back to your regular schedule thread..

  11. #9
    mo balls than $cents$ IMPATIENT 1's Avatar
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    maybe the pick up in rpms is cavitation. 120lbs more weight in the bilge area will require hardware changes, my gullwing did when i went from the blown 475 to the nitrous na 505.i could pull a new amt ss to 7300 on nitrous if my pump wasn't loading well at speed, and i didn't have the hp/tq to be doin that, and my pump was tighter than a bullfrogs ass when i knew i was into a good pass, my pump would turn around 6800, and 35-40psi on the intake. something other than the motor set-up has changed, but it may just a hardware issue that needs attention.all that hp in the world's not gonna help if its dragging transom from the addition of the new weight.

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  12. #10
    What the Hell is That? 72Hondo's Avatar
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    Quote Originally Posted by IMPATIENT 1 View Post
    maybe the pick up in rpms is cavitation. 120lbs more weight in the bilge area will require hardware changes, my gullwing did when i went from the blown 475 to the nitrous na 505.i could pull a new amt ss to 7300 on nitrous if my pump wasn't loading well at speed, and i didn't have the hp/tq to be doin that, and my pump was tighter than a bullfrogs ass when i knew i was into a good pass, my pump would turn around 6800, and 35-40psi on the intake. something other than the motor set-up has changed, but it may just a hardware issue that needs attention.all that hp in the world's not gonna help if its dragging transom from the addition of the new weight.
    I was thinking the same thing. weight added in that area i would think will make it ride a little deeper in the water. It looks like a heavy hull with the hatch back there and everything. A droop may help to rise the transom some out of the water. But then again 100lbs does not sound like a whole lot.

    don't know much about the boat Pump wise. When you GPS'd it the first time what were the conditions? Chop? 11 people on board? full tanks?
    Quote Originally Posted by Kyle View Post
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  13. #11
    Senior Member cruzer's Avatar
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    Cave,

    From the videos it appears that the water has been kinda flat. Maybe you need a couple of wakeboarders to chop up the water a bit. Also, you have been running with a co-pilot and he doesn't appear tp be a lite-weight (no offence meant to Marko). Was your 73 mph run just you in the boat? Were you nearly empty on fuel? Was there a bit of chop on the lake? What about a tail wind? Were they letting a lot of water out at the dam that day? Many things can effect top speed. Add another 100 pounds of weight to the motor area and see how much that changes your speed next time yo go out. Use sand bags so you can empty them without risking an environmental catastrophy(sp?)
    Cruzer
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  14. #12
    Senior Member moneysucker's Avatar
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    Swap the pulleys and see what that does for you.
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  15. #13
    mo balls than $cents$ IMPATIENT 1's Avatar
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    Quote Originally Posted by moneysucker View Post
    Swap the pulleys and see what that does for you.
    my 12.5 to 1 468 made about 150hp less than my blown 475 underdriven and would almost do the same mph, until i went 19% over

    Dare to be different, if it turns out great you can claim you planned it that way.

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  16. #14
    Senior Member ol guy's Avatar
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    Quote Originally Posted by cave View Post
    Summary, I spent the last 4 months rebuilding the engine. I added a 6/71 blower. With the intake & carbs, I would say the two weigh somewhere around 100lbs. Before the Blower. At 4900 rpm the boat ran a solid 73 + on GPS. Now with the blower, 4lbs of boost (8% under driven) 5500 rpm the boat runs 69.9 on gps.

    If I now picked up 100 extra pounds but increased the rpms by 6k should I be at least equal to what I was running?

    I did change out the cam for a blower friendly cam with less duration.

    If I increased the rpms shouldn't I have a bit more speed or is that 100 lbs extra that much more a negative than a positive???

    I have a thread in the West Coast South that show the build. Oh and the videos that I show with me running the engine are with the PTO disconnected.
    Cave, Just swap the pulleys and let the blower do it's job. M

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