Engine Build Advice
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Engine Build Advice

  1. #1
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    Default Engine Build Advice

    Have a 21FT daycruiser with a 468BBC 12JC Pump.I want to try and get 60 to 70 MPH out, of this boat I believe the horsepower now is in 320 Range I think 450 to 500Hp is what i need to achieve this goal using pump gas Technical advice on a modest budget Is this goal possible

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    Adding a place diverter will get you a bit more

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    Senior Member speedealer's Avatar
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    My 21ft sleekcraft runs mid 60s at 5000ft. the engine is 482 10:1 comp, ported small ports with 219/188 11/32stem valves,solid roller 250* at .050 .650 lift, had it ground on a 106lc, team G intake for a dominator with adpator for 850, msd ign. imco exhaust. the pump is a berkley with a aggressor aa,droop, and diverter. don't know how much hp never been dynoed. good luck with what ever you build.
    Last edited by speedealer; 03-17-2011 at 07:45 PM.

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    Look at the reply from speeddealer. Before anyone can help with where to go, you have to know where you are starting from. Need your boat information. Engine information, hull weight and jet details such as what impellor you are running along with current max rpm and boat speed you are able to do now.

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    "BOATLESS" blender over's Avatar
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    Quote Originally Posted by learmec View Post
    Have a 21FT daycruiser with a 468BBC 12JC Pump.I want to try and get 60 to 70 MPH out, of this boat I believe the horsepower now is in 320 Range I think 450 to 500Hp is what i need to achieve this goal using pump gas Technical advice on a modest budget Is this goal possible
    A 21ft day cruiser is going to need more then 500 hp to get to 60 on a gps.

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    Senior Member splatter's Avatar
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    Quote Originally Posted by blender over View Post
    A 21ft day cruiser is going to need more then 500 hp to get to 60 on a gps.
    I don't think so. I have a 21 ft Carrera that just hits 60 and I know it doesn't have 500 hp. Maybe low 400's.

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    "BOATLESS" blender over's Avatar
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    Quote Originally Posted by splatter View Post
    I don't think so. I have a 21 ft Carrera that just hits 60 and I know it doesn't have 500 hp. Maybe low 400's.
    Has the motor been on a dyno. Or the boat on a gps?

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    "BOATLESS" blender over's Avatar
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    Quote Originally Posted by splatter View Post
    I don't think so. I have a 21 ft Carrera that just hits 60 and I know it doesn't have 500 hp. Maybe low 400's.
    So let's say 425hp, 21ft day cruiser, 60mph?

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    Senior Member splatter's Avatar
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    Quote Originally Posted by blender over View Post
    Has the motor been on a dyno. Or the boat on a gps?
    That's 60mph on GPS. The motor has never been on a dyno, but knowing the basic parts in the motor it can't be much over 400hp if that. I think the Carrera has a pretty good bottom for a big boat and it has a good pump and setup.

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    "BOATLESS" blender over's Avatar
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    Quote Originally Posted by splatter View Post
    That's 60mph on GPS. The motor has never been on a dyno, but knowing the basic parts in the motor it can't be much over 400hp if that. I think the Carrera has a pretty good bottom for a big boat and it has a good pump and setup.
    wow you should be proud, would have never thought! But then again it is a Carrera so it's barley considered a daycrusier in my book.
    Who did your pump work?

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    Senior Member splatter's Avatar
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    Quote Originally Posted by blender over View Post
    wow you should be proud, would have never thought! But then again it is a Carrera so it's barley considered a daycrusier in my book.
    Who did your pump work?
    GS Marine. Come on now. It's 21' and has a little hump on the deck. It qualifies as a daycruiser. On the other hand, I had a Dimarco cruiser (Spectra copy) that was built like a tank. I don't think I could afford to build an engine to get that thing to 60. Great boat, just very heavy.

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    Modest price? You are doomed! The minimum motor to be considered is a 496 with small square or oval port aluminum heads, hyd rlr cam, some good valves (about $250 worth), precision machining by a reputable ENGINE shop that KNOWS boat motors. Nothing less will do the job or last very long. Clearances and cams are very different in a boat rather than a car. A 500 HP engine in a car runs high 10s or low 11s in the quarter mile, so how long can you stay on it? 10-12 seconds! Every day at the lake we see peeps idle out of the 5 mph zone and run wide open for MILES! I warm mine up longer than that til the oil temp is up, but then I do it too. Cut corners on parts, machinework, or expertise and you will have junk. P.S. use forged pistons only, NOT hypers, or forged head relief hypers either. Plan on spending about $5500.00 minimum on the long block, or reconsider your goal. Welcome to the real world. TIMINATOR
    MODESTY IS A CRUTCH FOR THE INCOMPETENT!

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    "BOATLESS" blender over's Avatar
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    Quote Originally Posted by TIMINATOR View Post
    Modest price? You are doomed! The minimum motor to be considered is a 496 with small square or oval port aluminum heads, hyd rlr cam, some good valves (about $250 worth), precision machining by a reputable ENGINE shop that KNOWS boat motors. Nothing less will do the job or last very long. Clearances and cams are very different in a boat rather than a car. A 500 HP engine in a car runs high 10s or low 11s in the quarter mile, so how long can you stay on it? 10-12 seconds! Every day at the lake we see peeps idle out of the 5 mph zone and run wide open for MILES! I warm mine up longer than that til the oil temp is up, but then I do it too. Cut corners on parts, machinework, or expertise and you will have junk. P.S. use forged pistons only, NOT hypers, or forged head relief hypers either. Plan on spending about $5500.00 minimum on the long block, or reconsider your goal. Welcome to the real world. TIMINATOR
    ? I think you posted in the wrong thread. LOL

  16. #14
    Senior Member River Dad's Avatar
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    There is definately a huge difference among 21 daycruiser hulls. Some are built like tanks with warped bottoms and others are not as heavy with good bottoms. A little more info about the boat and some pics would help. 60 is probably doable but 70 would be a huge push and a good chunk of change. pics of the current set up (and exhaust) would help. If you are running standard logs, add the cost of a new exhaust system as well. Good luck with it, and there are lots of really good info sources on here to get you to your goal. RD

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