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Thread: any one modded a 25hp merc?

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    Default any one modded a 25hp merc?

    has anyone modified a 25hp merc? from the 1990's with the 2.25 gear ratio

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    Team Member genea01's Avatar
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    Default merc

    what kinda boat u running it on

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    a winrace from Europe hopefully, www.winrace.no/index_eng.php

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    Team Member JohnsonM50's Avatar
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    Default Winrace

    Quote Originally Posted by ber1023 View Post
    a winrace from Europe hopefully, www.winrace.no/index_eng.php
    Is this one yours? [lake Hopatcong last fall]

    Theres several ways to look at making it faster. 1, Setup of motor/boat, height, angle, weight & its distribution. 2, Prop choice, a general prop made for the motor might not be working to potential. Luckily Merc offered performance options but a custom prop may be needed. 3, HP/RPM. mods can always be done but with 2 1/4 : 1, if you got 1,000 more R's out of the powerhead it would add up to about 5 MPH if you were using a 13" pitch prop. Larger pitch could increase that a little but its easy to over pitch a small motor & lose performance. Its being a deep V [?] is hard for the motor, they can be fast but it takes more.

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    no, same boat though I live in Bermuda. Yeah ill have winrace prop and the boat set up properly i just want to mod engine!

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    IF your block has the word "Mercosil" cast into it (upside down and on the right rear side) then it can be safely ported. (The earlier, chrome or nickel plated bores are "iffy" since the plating can peel away.) Since the heads don't come off, any raising of the exhaust port will result in a loss of compression ratio, but that motor is very mildly ported so.... I'd say it's worth a try.

    I can tell you from my own Merc 25 experiments that merely slapping a larger carb on does very little.

    Jeff

    PS: Nice boats!

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    Team Member JohnsonM50's Avatar
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    Quote Originally Posted by Fastjeff57 View Post
    IF your block has the word "Mercosil" cast into it (upside down and on the right rear side) then it can be safely ported. (The earlier, chrome or nickel plated bores are "iffy" since the plating can peel away.) Since the heads don't come off, any raising of the exhaust port will result in a loss of compression ratio, but that motor is very mildly ported so.... I'd say it's worth a try.

    I can tell you from my own Merc 25 experiments that merely slapping a larger carb on does very little.

    Jeff

    PS: Nice boats!
    It can be looked at as HP per CI. you can increase HP on the same CI's by trading off low end power. Motorcycles can run well with incredible HP per CI because of 4,5,or 6 gears. Outboards need the low end so while maybe not hi performance in comparison at least performance engineered. Stock Race outboards give a little more power at the motor usually but the reduction of running friction & spinning a smaller prop at higher RPM's is what makes them work. If you went that direction you might gain 10, 12 MPH's [give or take] The 1 in the pic is real nice, great cockpit & looks like alot of fun but the typical varied wood hydro's runabouts there were faster.

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    it doesnt have "merosil" on it, whats the best motor in this size and weight range to modify and get the most power?

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    Team Member genea01's Avatar
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    Default ??????

    what is the ci range int he rules

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    no rules, im not racing its just pleasure basicaly. All racing in bermuda has died out more or less

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