Thread: Johnson "70mod"

  1. #121
    Team Member hupiveneilija's Avatar
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    Dont know, meter is at work. But must be low because it works so good.
    Did math and it gave 7.2 cr. From the point ex chamfer closes.

  2. #122
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    will be interesting finding out what the rpm is and the cold cranking compression psi..
    but so far it seems as though its a very powerful motor.

  3. #123
    Team Member zul8tr's Avatar
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    Quote Originally Posted by filthy phill View Post
    what is compression, cold cranking all 3 plugs out and NO oil put in the bores, cannot get proper reading if putting oil down the bores.
    And throttle full open.
    " Three may keep a secret if two of them are dead" Ben Franklin

    Location: SW Orlando, Fl

  4. #124
    Team Member hupiveneilija's Avatar
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    Quote Originally Posted by zul8tr View Post
    And throttle full open.
    Always

    Installing new tachmeter so dont have to guess how much over.

  5. #125
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    throttle open or closed dont make any difference at cranking speeds, air comes straight back in from exhaust anyway.
    ive often measured compression with and without fully opening the carbs and it dont make any difference.
    I have even put a plate over the intake to seal it just to see what happened, no difference at all.. there is no explosing sending hot exhaust out in a hurry.
    and obviously no one way vale closing the exhaust port, so it realy dont make a difference.
    but do it what ever way you want, as long as you get the reading with it cold with no oil or fuel dumped in the bore to give a false reading.

    on a 3 cylinder I always double check if its been left a while, but with this just having the pistons and rings out it will not be any sticky rings.

    but be good to see how high or low it is.

    and to see how high the rpm is , then can get an idea of how long the motor will last..

  6. #126
    Team Member LittleCharger's Avatar
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  7. #127
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    I see its 190 psi, but what motor is this on ?
    is this a modified 56 omc ? how much taken off the head ? 80 thou ?

  8. #128
    Team Member LittleCharger's Avatar
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    Quote Originally Posted by filthy phill View Post
    I see its 190 psi, but what motor is this on ?
    is this a modified 56 omc ? how much taken off the head ? 80 thou ?
    Bridgeport, combination of things not just head, stock heads vary a lot any where from 30.5cc to 34.5 cc, some commercial heads are 42 cc, so it just depends on the head

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    Team Member hupiveneilija's Avatar
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    Quote Originally Posted by LittleCharger View Post
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    I have same meter now. It must be faulty because it shows way much lower numbers. 145, 146, 135.

  10. #130
    Team Member hupiveneilija's Avatar
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    Quote Originally Posted by LittleCharger View Post
    Bridgeport, combination of things not just head, stock heads vary a lot any where from 30.5cc to 34.5 cc, some commercial heads are 42 cc, so it just depends on the head
    I measured also heads from 30 to 34 and my small chamber 21.
    That 190, is ex port in stock timing? I have chamfer, 1.382 from deck.

    My motor feels real good when running even its quite worn. White one when bored and built with new pistons 5 years ago wasnt nothing like this now. Think that crank psi isnt the hole truth as you go on higher rews. Big part of the story is scavening and how it works.
    I think Ill try little more ign timing when go out next time. A degree or two. IMO my previus PH wasnt up to task, not even if I had limiter taken away, because it was just under that and was hitting occasionally.

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