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Thread: 56ci OMC realistic power

  1. #61
    Team Member hupiveneilija's Avatar
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    Yes i know. Now i have same ph in place with shortened tuner, no proplem on going plane. Have to see how it goes when i get jetting right.
    And im short of prop for now.

  2. #62
    Team Member skeg's Avatar
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    Great thread

  3. #63
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    its surprising how an engine thats been around for 30 years still gets so much interest and is still about the best bang for its size.
    I know mercury have their 60 that can be hotted up, but it still cant beat a real hot 56, and out last it in normal recreational guise.

    when anyone says johnson or evinrude the mind thinks of the mighty 3 cylinder,
    when people say mercury you automatically think of the tower of power,
    when they say Force it reminds you to take out the rubbish .

    /

  4. #64
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    The thing that gets the mercury 60hp 3 cylinders which started as 53ci roughly then got bumped to 59ci in the late 90's was they were a blind bore so you can't shave the head to bump compression up easily. They were good engines I had a early 90's 60hp merc for a little while didn't hop it up at all but it ran well. The omc triples are just hard to beat for the power to weight and price. The larger three cylinder yamaha's are great the 70-90hp ones, but I don't have one because they seem to command pretty high dollar for a good one. Enough so for a decent tiller version that I would almost just consider a new FI four stroke as much as I hate to say it. That and I've just been partial to omc starting with my first outboard I acquired in college for nothing was a 1965 johnson 9.9 that I fixed up and used through most of college hunting and fishing. I beat the hell out of that motor friend of mine still has it and uses it to this day on a little fishing/hunting boat. All I did on it was replace points rebuilt the carb and she never failed. After that I had 1975 25hp johnson, then 1988 johnson 40hp two cylinder, then a nissan 40hp three cylinder, then the merc which I put a jet lower on, and now the evinrude 70 which I'm wanting to mod some. Hadn't modified any of my outboards in the past just repaired them. Just about all of them didn't run when I first got them. Sorry I still haven't gotten to measuring the carbs on my engines I need to just been busy moving things, working on and fixing up the new place you know that annoying thing known as life that gets in the way of fun stuff.

  5. #65
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    yeah I had one of the 1991/2 model year mercury 60hp, fantastic engine idled great ,good amount of power and surprisingly good on fuel.
    u did not know until I got it that the heads could not come off or would never of got it.
    But it came on a boat /engine trailer package that was all like new for a good sensible price.
    I have had a few of the 49ci omc and can say that they were more powerful than the merc but not as smooth on the idle and all around reliability.
    I find the 1995 oval port 56 miles ahead of the mercury 60 of the early 90's and also more powerful than the later mercury offerings.


    with your lower unit being a jet, if you modify the motor for more power you can just have the impeller in the jet pitched up a bit to give more speed and thrust.
    from what I have read too many rpm is not a good thing for the jet housings/bearings ?? dont realy know about that as plenty of the jets went into military use.

    its nice when people on here walk you through everything they have done to the powerhead to get the realy high power from the motors, but we need to
    remember that most of these guys race and are not worried about re-building every few weeks (sometimes each race meeting).
    I like longevity and just a little more power and put a lasting engine 1st.
    A lot of the performance on the motors seems to come from just cleaning stuff up like bad casting marks, this can only be a good thing for any motor.

  6. #66
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    Tried to make a new thread but the forum is not letting me
    today I measured port specs on my oval port spare block. I got some very surprising results and measured it loads of times to make sure of accuracy.
    What I found might help some people who are looking to modify their oval port, and or save them stripping one down to see what is in there or not .

    I measured all the ports on my 1995 oval port 56 motor. Cylinder block part number 0436908
    I have read on a few places about how much smaller the oval exhaust is compared to the bridgeport exhaust. !!!....err thats is not exactly true if we are talking of area of the exhaust ...
    Maybe some blocks are different ? I dont know and can only say what is here is exactly what I have in front of me.

    The standard fishing motor oval exhaust is WIDER than the sst60 spec for APBA, the other ports are also slightly wider. ?
    here is the results
    sst60 exhaust width of each port is 1.075 x 2 = 2.150..........oval exhaust width is 2.185039 ( 30.5 thou wider )
    sst60 Boost port max width is 1.255...................................oval port boost port is 1.29921. ( 44 though wider )
    sst60 Transfer port max width is 1.5800........................... oval port Transfer width 1.633858. ( 55 thou wider )

    Some of the heights of the ports on SST60 are higher by a fair bit , but there is room to take any or all of ports to the same height.

    Sst60 exhaust port height is min 1.450 and max height 1.520...........oval port height is 1.500 standard ( lower by 50 thou )
    sst60 boost port height min.....1.860 and max height 1.950..............oval port boost port height 1.88976 ( within sst60 spec )
    sst60 transfer port height min. 1.825 . and max height 1.890...........oval port transfer port height 1.948819 ( lower by 104 thou)

    Not sure if the sst60 measurement for transfer top is with or without chamfer ???

    exhaust and transfer port roofs are up a fair bit higher than the sleeves, so are capable of being taken up to sst60 spec.


    Going by these measurements, with a bit of work on the exhaust and a touch on the transfer port height, the oval port would be able to breath a lot better.


    ALL the ports behind the sleeves need to be cleaned up a lot and the sleeves themselves have some terrible edges on some of the tops of the ports that are
    more like a serrated knife edge than a proper nice clean port, they definitely could do with cleaning up.
    OMC did not take any care when assembling the 56 oval port motors, no attention paid to detail at all.
    Sleeves look like they have been put in without them being finished off.

    The exhaust outlet to afaptor from the bottom of the block itself needs to be cleaned up inside as far as possible to get rid of some very bad casting
    marks, this can be done with a small flexible shaft and small wire brushes/wheels etc, not an easy task but it would pay off big time to let the gases flow better.
    with the use of a tiny endoscope ( very cheap on ebay with 6 built in lights) a lot can be done to the exhaust as in polish it up to flow better.

    for those who might be interested, I have made a sort of port map drawing to show the oval port versus the SST60 spec for APBA rules..
    ( nothing like true map or scale) just to show the port sizes and heights. sst60 specs in the blue boxes.
    Attached Images Attached Images  

  7. #67
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    For anyone interest here below is a diagram of the port heights on the 56 ci Oval port motor from 1993 onwards ( not to scale ) it shows
    the oval port heights and SST60 heights.
    Also showing some recommended heights (m.w) to allow it to rev higher and raise the powerband range.

    .
    Name:  omc 56 port dims.jpg
Views: 1391
Size:  283.7 KB

  8. #68
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    I believe I still have the port angle gauges I used when porting this engine while working for the OMC race group years ago . i do not remember the exhaust port beging oval like that ? when I did it it had more of an " eye brow " shape to it.. the exhaust chamfer looks good ...
    Likes Freddie Webb liked this post

  9. #69
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    No the port is not that shape, thats only my drawings , dont take too much notice of the shape. I am not an artist by a long way ha ha
    here below is a real pic of the Exhaust port.
    with this pic you can clearly seethe bottom is a lot narrower than the top, I think keep similar shape just go wider with the port by about 1.5 to 2mm each side,

    Below the Exhaust Port pic is a picture of the Boost Port, and this shows the wonderful "Glue Lines" strategically put in by OMC to keep everyone happy !!!

    .Name:  20170219_145500.jpg
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    .
    .

    Here is the things so many people talk about, the dreaded "GLUE LINES.. these realy are a problem and are on all the 56 oval ports, all the bridgeport motors made by the
    lost foam process including the sst60 motors. these glue lines are pretty easy to get rid of, just as well because there are loads of them in the blocks that can all be got rid of.

    .Name:  Boost port and glue lines.jpg
Views: 1335
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    .

  10. #70
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    Davidblanchard
    you said "I believe I still have the port angle gauges I used when porting this engine while working for the OMC race group years ago"
    Does this mean you had a race version of the oval port motor in the planning ?

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