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Thread: Johnson "70mod"

  1. #1
    Team Member hupiveneilija's Avatar
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    Default Johnson "70mod"

    Here are couple of pictures for powerhead. I have also weighted rods and pistons, they are within .5grams the same. Crankshaft and flywheel are on the way.
    Attached Images Attached Images      

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    Team Member LittleCharger's Avatar
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    Are you going to blend the exhaust ports in the pic it looks like some mismatch still between block and sleeve.

    will be interesting to see how those heads work. You may need head studs if the compression is real high as then tend to blow head gaskets without them

  3. #3
    Team Member hupiveneilija's Avatar
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    They are matched, picture may lie. I dont know what psi will be but head maker did it so that the compressionratio is aprx. 7.2:1, i think, with stock ex.port. Since I have raised the ports its lower now.
    edit; I think he said that stock comp ratio was 5.9:1.

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    what is that metal wall behind the exhaust bridge ?
    not seen this before, my block definitely dont have a wall behind the exhaust port.

    did you put this there ?

  5. #5
    Team Member LittleCharger's Avatar
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    Quote Originally Posted by filthy phill View Post
    what is that metal wall behind the exhaust bridge ?
    not seen this before, my block definitely dont have a wall behind the exhaust port.

    did you put this there ?
    Stock

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    what ?
    are you saying this is normal for the 56 bridgeports to have this thick dividing wall in the exhaust behind the liner ?.

    so this means the blocks used for bridgeports are not the same as oval port and sst60 motors.

  7. #7
    Team Member hupiveneilija's Avatar
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    Its the same lostfoam cast as sst60.

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    its is cast in the same way as SST60 yes, but it is NOT from the same casting as the 60/70hp fishing motor. they are different.
    plus the sst60 also different height of block from top to bottom.. piston go over the top of the block on sst60. they do not go higher on normal block.
    different casting numbers on the blocks too.

  9. #9
    Team Member Hevi Kevi's Avatar
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    Quote Originally Posted by filthy phill View Post
    its is cast in the same way as SST60 yes, but it is NOT from the same casting as the 60/70hp fishing motor. they are different.
    plus the sst60 also different height of block from top to bottom.. piston go over the top of the block on sst60. they do not go higher on normal block.
    different casting numbers on the blocks too.
    Phillnjack - I mean Filthy Phill,
    The reason the deck heights are different and pistons stick up past the deck is from people machining them to the minimum specs and using the longest allowable rods and cranks with maximum throw allowed. The bridgeport blocks are the same. Different sleeves. It's called a bridgeport because of the bridge in the middle of the exhaust port. The oval port is called an oval port because of the oval shaped exhaust port.

    Kevin
    Critchfield 15" 56ci OMC
    RapidCraft Cyclone 15" 56ci OMC


  10. #10
    Team Member Hevi Kevi's Avatar
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    hupiveneilija,
    Did you have any problems with the head warping when you welded up the chambers?

    Kevin
    Critchfield 15" 56ci OMC
    RapidCraft Cyclone 15" 56ci OMC


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