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Thread: Omc 3 cylinder comparison

  1. #11
    Team Member TBuck2003's Avatar
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    56 for sure has more grunt. As far as set up ,and performance the short mid with the nitro case is the way to fly. The big case on that boat does not run well, and the long shaft hampers set up. Have same boat with 49 ci with shorty and Nitro case. Pic is in my avatar. My .02

  2. #12
    Administrator Ron Hill's Avatar
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    Default 56 vs 49

    I think I have made a deal to get Bunker Hill's old three banger from Mickey Schwarzenbach form Apple Valley Marine.

    I'm not talking about my "PROJECT" here, but do want to know how much performance difference there is between the 49 and 56???

    Second part of my question: Anyone know how many 49 ichers were made? And how many 56 inchers were made???

  3. #13
    Sam Cullis Mark75H's Avatar
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    IF anyone knows, its probably Edgar
    Since 1925, about 150 different racing outboards have been made.


  4. #14
    Team Member TBuck2003's Avatar
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    I am in need of some 56-58d jets for a 1976 Evinrude 75 "S" short shaft. I think they came with 55d but that is at 16* timing. PLEASE send a PM or respond if you have any or know of any...Thx

    Todd

  5. #15
    YARD BIRD
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    Default Jets & timing

    Back in the day, (1975) Tom Ireland ,after much trial &error, came up with optimum settings for the 75 (short shaft ) in closed course competition. 1 step leaner jets & 3 MORE degrees timing ;19 degrees before tdc.He also said that you must be propped to turn 7000
    R P M or you won't be competitive......the early 1975 75horse motors came with a higher compression head than than 1976 motors. check the parts lists. there was also a higher compression head (optional) available and legal for the Sport E tunnels &family E runabouts.
    I am refering to about sea level altitude.

  6. #16
    Team Member mercmack's Avatar
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    Talking Omc jets

    All you need is a real omc factory service manual..in the back of section 2 or 3 they list all the jets they used in all there late model motors ..it has the jets size and the part no that goes with it....a parts list will give you the part no for the standard jet then use to s/m to pick out the jet you want and order it from any body that can get omc parts..:d

  7. #17
    YARD BIRD
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    [QUOTE=Roy Hodges;96564]Back in the day, (1975) Tom Ireland ,after much trial &error, came up with optimum settings for the 75 (short shaft ) in closed course competition. 1 step leaner jets & 3 MORE degrees timing ;19 degrees before tdc.He also said that you must be propped to turn 7000
    R P M or you won't be competitive......the early 1975 75horse motors came with a higher compression head than than 1976 motors. check the parts lists. there was also a higher compression head (optional) available and legal for the Sport E tunnels &family E runabouts.
    I am refering to about sea level altitude.......................................... .................................
    .................................................. .................................................. ................................
    .................................................. .................................................. .................................After checking my notes from Tom; he said ".059 main jets are optimum &of course the 19 degrees before tdc timing." (sea level) These settings are for a legal stock 75 Hustler.

  8. #18
    phillnjack
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    Here is a pic of a 56 head with the flat for the plugs like mentioned above
    as for the head and water jacket being one piece, the water jacket does look like it should come apart, but it dont.
    the thermostat housing also different to 49in
    below is a pic of the head on my 56 in, on a 1995 evinrude engine.

    Name:  56 in head.jpg
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    phill..........

  9. #19
    Team Member Smokin' Joe's Avatar
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    Old post but so what. Not much hp difference between 49.7 and 56 c.i. powerheads,
    far more speed difference in nitro vs clubfoot gearcases. The later
    are geared so low you can't make them run.


    Quote Originally Posted by PIP View Post
    My 13 Allison (1972) is being restored as I get time, transom, core, the whole shabang. I have a question;

    I have an old (1980 ish) 75 OMC, not a nitro-cased motor and it has always been preached to me that it would be best to have a nitro motor, due to the 15 inch mid, as well as, narrower gear case. It is also my understanding that the later 56 inch race motor, is even better, but my question is; if I cannot readily purchase an old nitro motor, or a later racing 56 incher, wouldn't the standard later 56 inch, 70hp motor be better than what I have, and as far as top end goes, wouldn't it also be better than the 49 inch nitro motor, simply because it puts out so much more power?

    I am cost consious and not doing any sanctioned racing, but like to go fast. It simply seems that their is no good reason for me to spend $2,000 on a good nitro 49 incher, if i can pretty easily spend, $800 on a good, late 1980's 70hp that is "faster" still, though it will lack the 15 inch, on top end, I see this making little difference.

    Thoughts please?

  10. #20
    phillnjack
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    well i have to disagree about the 56ci not being much more power than a 49ci.
    ive had both 49 and the 56 inch motors both 60hp versions, i find the 56ci to be a lot more powerfull and responsive.
    maybe its just the two engines ive owned ?

    what exactly is a nitro and what is a clubfoot ? coz i dont think we get them over here.



    phill

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