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  1. #1

    Default Mercruiser 496 base: HP upgrade

    OK. I have a base 375 hp merc 496 that is reliable and causes no issues. So being the speed idiot I am, what are the options are a 50+ HP upgrade? more questions to follow. What I have read ( and believe)...
    Raylar... Nice, but don't mess with a stock motor. If you want a big increase in power go with a motor swap.
    Ok. So a motor swap... What will plug and play into a 496 that is reliable.
    What is reliable?.... 750+ hours with excellent reliability.
    Back to the questions to follow: What will 500+ HP do for a 25 foot Glastron GX 255? Better low end? Better top end?
    Standard duo-prop 28P on it now.

  2. #2
    Join Date
    Dec 2006
    Location
    Chaumont Bay, N.y., USA
    Posts
    5,218

    Default Re: Mercruiser 496 base: HP upgrade

    Ayuh,.... Bein' an electronic Efi motor, yer options are extremely limited,...
    Any Grease is Better,... Than No grease at All....

  3. #3
    Join Date
    May 2010
    Location
    DC Burbs/Maryland Eastern Shore
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    1,127

    Default Re: Mercruiser 496 base: HP upgrade

    Try some prop tuning. You may be able to squeeze a bit more from it. Generally speaking. the engine should be turning around 5000 rpm at WOT. If it is more, then you may go up one step at a time with the props or increase the diameter and keep the same pitch. If you are below 5K, then you need to reduce the pitch size one step at a time until you're there. Prop tuning is a black art, and the other things to consider are payload, ballasting, trim, hull shape, and slickness of the bottom finish.
    A good prop service will come to you with several combinations for you. You have to change the props, go do a measured timed run, change again, repeat, repeat repeat until you hit on the right one.
    Adding horsepower does not necessarily improve things all that much. Let's say you drop...I dunno...$7500 on engine improvements like a cam and big exhaust. You get an additional maybe 30 horses. OK so now your WOT is say 5100 instead of 5000. That will allow you to gain maybe 2 or 3 more knots at the top. Worth it? you tell me.
    If you want a 500 HP engine you are talking forced induction. You might as well start now saving up for your next engine cz this one will last you maybe a few seasons before it needs to be replaced. Dunno how long a marine supercharger is supposed to last but I imagine not long.
    Practicing the ancient art of ren-ching

  4. #4
    Join Date
    Nov 2005
    Location
    Mt. Zion, Illinois,
    Posts
    528

    Default Re: Mercruiser 496 base: HP upgrade

    Quote Originally Posted by o2batsea View Post
    Try some prop tuning......Prop tuning is a black art, and the other things to consider are payload, ballasting, trim, hull shape, and slickness of the bottom finish.
    Good things to consider. Engine upgrades get spendy quick and can introduce reliability issues.

    Does the boat have trim tabs? I've found those to be enormously helpful out of the holes and also to improve bow lift while on plane.

    KJ

  5. #5
    Join Date
    Dec 2006
    Location
    Chaumont Bay, N.y., USA
    Posts
    5,218

    Default Re: Mercruiser 496 base: HP upgrade

    Good things to consider.
    Ayuh,.... Unloadin' the boat can do Wonders,....

    How much junk ya got stashed in the cabin, that you've never used,..??
    Any Grease is Better,... Than No grease at All....

  6. #6
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,824

    Default Re: Mercruiser 496 base: HP upgrade

    If you're willing to trade some service life for some performance, a "custom tune" is probably the best bang for the buck....

    if you want more than a few knots of speed, better off getting a different boat.....big engine(s), optimized drivelines, etc....speed ain't cheap, especially on the water....

  7. #7

    Default Re: Mercruiser 496 base: HP upgrade

    I sort of already knew the answer but wanted to hear from the experienced guys. I will leave it alone! Always the best choice when everything is working and no appreciable difference (for the $) in performance. Yes, I am getting 5000 rpms at WOT now with 28Ps. Thanks for your responses.
    By far the best response is from Bondo because your image is hilarious!!!!

  8. #8
    Join Date
    May 2010
    Location
    DC Burbs/Maryland Eastern Shore
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    1,127

    Default Re: Mercruiser 496 base: HP upgrade

    Don't rule out some prop tuning. The stock props are good, but there are high performance ones that you might be able to benefit from. Again, bet to call on the professionals for this. Usually their advice and testing are free when you buy a set of props from them.
    http://www.mercuryracing.com/boat-pr...ravo-three-xr/
    Practicing the ancient art of ren-ching

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