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Thread: Sweet 16 Top speed?

  1. #1
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    Sweet 16 Top speed?

    Just bought a 90 Sweet 16. It was a two owner boat and very well maintained. Replaced the original fuel pump with an electronic unit as the original was failing. Being my first Donzi I was wondering what this boat should do top end. I have only been able to hit 47.5 gps. Granted that was in a bit of chop 1 1/2 ft waves but I would think this boat would have a little more top end. It only has the 4.3 but still, trimmed out to the max I'm surprised it isn't a 50 - 55 mph boat. Any advice? Oh and BTW I'm running a 14 1/4 21p viper stainless prop. I've included some pics of the boat just for fun. (Picked it up for 5600 so I'm not complaining just wish it had a bit more top end.
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    What RPM?

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    Rpm

    May have been around 4800 or so

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    what are the specs on the 4.3? that motor ranged from about 180 hp to 225 hp ?
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    Motor specs

    I believe it is 190 hp. I messed with the trim tabs and the trim and got it up to 50.4 gps the other night on glass smooth water but was only turning around 4700 rpm. Not sure what to try first?

  6. #6
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    you are probably close to the limits on that motor. they do run a bit faster in chop then they do on glass the hull gets up and on top .

    do you have the specs on the drive ratio ?


    MPH=$$$$ the rule of thumb is every MPH you want to increase = $1000. for the most part that is a good benchmark the first mph might be a bit less usually the right prop with tweaking is under 1000 but the 2nd mph and each one after that the rule is pretty close to on the money.

    What is your speed goal?

    let's say it is 60 mph thats 10 mph you would need to have a mild 350 built with good hi-po exhausts and a gear set change in the drive for 10k

    a smaller goal of 5 mph might be done with improvements to the existing motor heads intake 4bbl carb cam for 5k

    there is no magic bullet well maybe the closest thing to one would be a slick shorty lower
    When the sky is grey,look out to sea.
    When the waves are high and the light is dying,
    well raise a glass and think of me...
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  7. #7
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    Found a published test of a 16 with the 220hp v8, and they said WOT was 58.5 mph. That motor is heavier, making me think you are still a hair low of what you might be reasonably expecting. Maybe 1-4 mph low.
    "I don't have time to get into it, but he went through a lot." -Pulp Fiction

  8. #8
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    My 4.3 dyno sheet. It's a very mild build. I'm certain 300HP can be achieved (fairly easily) on one of these motors while keeping reliability.
    4.3 Dyno 05242013.JPG
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    Sean Conroy,
    1964 Formula Jr. (hull #2) project

    1972 Greavette Sunflash III
    1981 Kavalk Mistral project

    "A man can accomplish anything... as long as he doesn't care who gets the credit."

  9. #9
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    woobs what did the motor run you? with that increae in HP are you doing a gear change or are you going to run a bigger prop?
    When the sky is grey,look out to sea.
    When the waves are high and the light is dying,
    well raise a glass and think of me...
    When I'm home again,
    boys, I'll be buying!

    My Ride

    Come Join Us on The Queen Of American Lakes



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  10. #10
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    Quote Originally Posted by mattyboy View Post
    woobs what did the motor run you? with that increae in HP are you doing a gear change or are you going to run a bigger prop?
    I built the motor for less than 3K (incl. taxes). But, you have to add the $$$ for the Hi Tek exhaust.

    I run a 1.47 on an Alpha, Gen I (SEI) with a 19*Hi Five pulling prop. Unfortunately I'm still at 4,300 - 4,400 rpm and the motor should turn 5,200. I have 53mph on GPS with my 18' wooden boat (not built for speed). If I did it again, I'd go with a 1.65 drive and have more prop selection options.

    I believe this motor in a 16 with a speed prop will hit 60 with no issues.
    Greavette Sunflash IV July 2013 copy.JPGGreavette Sunflash IV July 2013 015.JPG
    I love the way this boat jumps up on plane and cruises at about 40mph all day (with 5 people aboard). I'm still considering moving to a 4 blade 19* Solas to get another 250-ish rpms and not sacrifice the great hole shot.
    Sean Conroy,
    1964 Formula Jr. (hull #2) project

    1972 Greavette Sunflash III
    1981 Kavalk Mistral project

    "A man can accomplish anything... as long as he doesn't care who gets the credit."

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    I used Vortech heads and 1.6:1 roller rockers, hypereutedic pistons, all new hardware (valves, bearings, springs, studs etc...) with a cam regrind. The engine is all stock dimensions and no porting has been done.

    Topped it with an Edelbrock 2114 "performer" intake mated to an Edelbrock 1409, 600cfm 4bbl "performer" carb. Stock Thunderbolt ignition.

    I kept the package as light as possible with the Hi-Tek exhaust manifolds and with an aluminum circulating pump, aluminum pulleys and anything else I could lighten.

    I added a custom baffled oil pan and tied everything together with braided steel lines and quality marine hose (w/stainless clamps).

    In it's entirety the package was just about 5.5K with taxes.
    Sean Conroy,
    1964 Formula Jr. (hull #2) project

    1972 Greavette Sunflash III
    1981 Kavalk Mistral project

    "A man can accomplish anything... as long as he doesn't care who gets the credit."

  12. #12
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    that is a nice setup and also brings out another part of the rule of thumb it can be less of a $$$ hit if you do more work yourself

    yes i would think 300 hp in a 16 without the added weight of a v8 would top out low 60s easy

    1.47 is the low v8 ratio I would think the cobra would be a 1.7 or 1.8 so with added HP the 21 he is spinning would need to be a 23-24 ish pitch

    what is the spec'd rpm at wot on the 190 motor?
    When the sky is grey,look out to sea.
    When the waves are high and the light is dying,
    well raise a glass and think of me...
    When I'm home again,
    boys, I'll be buying!

    My Ride

    Come Join Us on The Queen Of American Lakes



    Contact Us

    www.lgdonziclassic.com

  13. #13
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    Quote Originally Posted by mattyboy View Post
    that is a nice setup and also brings out another part of the rule of thumb it can be less of a $$$ hit if you do more work yourself

    1.47 is the low v8 ratio I would think the cobra would be a 1.7 or 1.8 so with added HP the 21 he is spinning would need to be a 23-24 ish pitch

    what is the spec'd rpm at wot on the 190 motor?
    I had this motor professionally built.
    I think the stock 4.3 Merc drive is 1.84. The spec rpm is 4,800.

    My calculations say a 1.7 drive with a 24* prop and 10% slip at 4,800 rpm should yield 57.8 mph.
    The 21 should yield 50.5 mph. So, his 16 is running "bang on".
    ...give or take
    Sean Conroy,
    1964 Formula Jr. (hull #2) project

    1972 Greavette Sunflash III
    1981 Kavalk Mistral project

    "A man can accomplish anything... as long as he doesn't care who gets the credit."

  14. #14
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    Nice looking package Woobs!
    2006 CLASSIC 18 WHIPPLED MX 6.2, BRAVO 1, STAINLESS MARINE EXHAUST, LATHAM STEERING, IMCO 2" SHORTY, LABBED MIRAGE PLUS

    TALK IS CHEAP, I'M FROM THE "SHOW ME STATE" SHOW ME

  15. #15
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    According to the chart it is a 1:51 OMC cobra drive, Chevy was a late year offering. I had an early 90 16 it had the Ford 302 same ratio drive, nice thing is a SBC will bolt RIGHT in an give it some real GO!
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    No matter what your beliefs are "GOD BLESS AMERICA"

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