Help With Horsepower Stock 454 Mpi
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Help With Horsepower Stock 454 Mpi

  1. #1

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    Default Help With Horsepower Stock 454 Mpi

    I Have 1996 22 Ft Donzi Classic With A 454 Mpi 385 Horse Im Looking For Ideas To Get More Horse Power I Have A 25 Pitch Mirrage And Can Only Get 4300 Rpms Out Of It Any1 Have Any Suggestions. I Dont Want To Spend A Fortune But Want A Little More Top End Any Advice Would Help Im New Here

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    Senior Member GT Jets's Avatar
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    Quote Originally Posted by 96DONZI View Post
    I Have 1996 22 Ft Donzi Classic With A 454 Mpi 385 Horse Im Looking For Ideas To Get More Horse Power I Have A 25 Pitch Mirrage And Can Only Get 4300 Rpms Out Of It Any1 Have Any Suggestions. I Dont Want To Spend A Fortune But Want A Little More Top End Any Advice Would Help Im New Here
    What type of exhaust, at what altitude, what top speed, what fuel, how much weight, and is the bottom painted (anti fouling)?

    4300 RPM seems a little low to me, this engine should be turning about 4700 RPM and not even breathing hard...IMO

    GT
    GT


    Quote Originally Posted by Quickjet View Post
    Put a 300 on the back of it, Flywheel it and a nosecone. $15,000 later you'll have a 65 mph pile of shit......

  4. #3

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    The Boat Weighs About 3700 Pounds It Has Silent Choice Thru Hull Exuast Stock Manifolds I Always Run It Thur Hull. Altitude Is Sea Level I Live In Miami Top Speed Is About 68 Mph. Do U Think The 25 Pitch Is To Much For It To Swing.do U Think If I Went Down A Pitch Or 2 More Rpms Will Make It Faster. Or Do I Need More Horse Like Headers Or Bigger Injectors. Im New To The Io Engines Always Had Outborad 2 Strokes What Do U Think
    Ive Only Had The Boat For 2 Months

    Thanks Nick

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    Senior Member GT Jets's Avatar
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    I would think pulling a 25" prop would be eaasily done unless it has a higher (numerically lower) gear ratio. This sounds stupid, but have you checked to make sure you're getting WOT at the throttle body?

    Something is wrong IMO, how tight is the engine cover, could it be starving for air?

    How does the boat ride (wet, aired out, plow) ? are there any defects in the hull? (anti fouling bottom paint?)

    Also sounds like a prop change is in order, but don't make sense, I would think it would pul the 25...That thing should run harder than that I think.

    GT
    GT


    Quote Originally Posted by Quickjet View Post
    Put a 300 on the back of it, Flywheel it and a nosecone. $15,000 later you'll have a 65 mph pile of shit......

  7. #5
    cfm
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    4300 is way to low of an RPM. I believe these motors are supposed to run around 4800-5000rpm.

    Since you may have to change props anyway, I'd ask the Donzi guys at http://www.donzi.net/forums/index.php if there is better type/style for your boat .

    No one knows a certain boat better than owners of a certain boat.

    Hope this helps.

    BTW: If your boat is propped wrong, spending money on engine performance parts will typically prove unfruitfrul and frustrating. Get it propped right, learn what the boat likes for props, and then with the new and improved speed and handling decide if you want more engine performance.

  8. #6

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    The Boat Rides Good And On Top Of The Water No Plowing The Bottom Paint Is Show Room Floor Gel Coat Looks Brand New Ill Check My Intake Again And Double Check Wot.im Going To See What The Donzi Guys Say Thanks For The Help Guys

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