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Thread: 1977 johnson 140hp crossflow mods

  1. #1
    pdt
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    Default 1977 johnson 140hp crossflow mods

    a friend of mine has a Johnson 140hp
    model is 140ml77s

    he /we would like to know what can be done to this engine to increase its power, and just howm uch power can these engines realy get to.

    we know that in 1977 the hp rating was at flywheel and is roughly 115hp to 125hp at the prop nowdays.

    ive heard of many of these engines getting huge speeds and power gains, but never knew exactly what can be done with one of these engines.
    before anyone says get a looper, a new engine is not going to happen, he would prefer to boost this one up, especially if he decides to completely rebuild it next year.

    so any info on this would be good, and ill pass it on.

    from what I gather these were 99 cu in motors !!!!! (could be wrong).


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    DaBull Dabull1919's Avatar
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    There are many mods that can be done but unfortunately at the expense of reliability. Things like scallop the bottom of the piston on the intake side 3/8ths for increased flow and match the block to the same cut. Lower the cc of each head for more compression with good high octain fuel. Square the ports but do not raise them. 140`s ports are high enough as is. If you can find an old set of mofified 10 port reed cages it will help. Lots of work for little gain. I would save my money and opt for a 150hp V-6 of the same make and year if possible. An early 80`s Johnson 150GT is a great motor.

    DB

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    pdt
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    the 150 is not much more power gain in the same year and about 130 pound heavier. so would be defeating the whole object.
    want to stay with same engine really.

    what were the specs of the sst100 engines ? of around same time.
    ive also heard these heads cannot be skimmed , the pistons would hit due to close already.

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    DaBull Dabull1919's Avatar
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    Yes they are too close to cut. Thats why i used the term cc the heads. It`s slang i guess for cc pading in areas that can hold some additional metal.
    The 150 is actually a 175 w/1 inch bore carbs and cut back timming. Put 1" 5/16"ths carbs from a 200 cross flow and set timming to 28 degree`s and presto chango you have a 175hp.
    I know your bud wants to stay with the 140 and i`m sure he has his reasons. It`s just a lot of work for such a small gain and after all the power head work you still can`t get a good high performance prop to fit because the prop shaft is to small.
    I`m telling you this so ya`ll won`t be suprised by it all later.
    Years ago we used OMC GP pistons in our 149ci V-6 to increase compression. I don`t know if anybody makes them today but maybe check with Wiesco.

    DB

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    Quote Originally Posted by pdt View Post
    the 150 is not much more power gain in the same year and about 130 pound heavier. so would be defeating the whole object.
    want to stay with same engine really.

    what were the specs of the sst100 engines ? of around same time.
    ive also heard these heads cannot be skimmed , the pistons would hit due to close already.


    .
    You can skim heads assuming you have access to good fuel but you will need to check clearance any usually the corners of the deflector are what hit but you can chamfer them a bit to gain clearance.

    SST 100 is a 2.0ltr looper only part in common are the sparkplugs
    If you want to play with a v4, although heavier, the looper is the way to go and better fuel consumption

  6. #6
    pdt
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    It`s just a lot of work for such a small gain and after all the power head work you still can`t get a good high performance prop to fit because the prop shaft is to small

    what ? diameter of propshaft being too small ?

    so basically your saying the 140 crossflow of 1977 cant be hopped up to kick out 150hp plus ? at the prop .

    seems strange that this is about the only engine that a big power increase just cannot happen.


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    DaBull Dabull1919's Avatar
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    I never said that a power gain cannot happen. All i did was to point out the problems with building a small motor. Since you asked then ok. Here it is. Buy a set of 1978 235 carbs and change the throttle blade shafts to V-4, Cut rod slots, scallop piston skirts and bottom of sleeve to match, Raise intake ports and square, Raise exaust ports and square, Stuff crankcase, buy 10 port reed cages, buy 135hp bypass covers, finger port block and pistons, Increase compression, Buy fuel to match compression, Install larger V-6 prop shaft, add nose cone w/low water pick up, open exaust in gear case. There are many recepies to do all of this and you will need a good machinest or contact a noted engine builder for old outboards that knows all the tricks. Maybe Monty Racing in Jacksonville, Fl. Ask for Gordon or Johns Custom Marine in Cali. Ask for Allen.

    DB

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    Nice formula...
    you forgot the machine block where the exhaust comes back in from the bubble to same as 135

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    pdt
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    what exactly is the difference between 135 and 140 bypass covers ?

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    Administrator Ron Hill's Avatar
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    Default Hill Marine Makes Performance Propellers for 140 Johnson and Evinrude with 13 Splines


    I
    I have been putting 13 spline rubber hubs in Choppers and Cleavers for more than 30 years. But now days, with he removable hub kits, switching for Fat shaft to 15 spline to 13 spline is a three minute job. Check m E-Bay store at http://www.ebay.com/itm/Evinrude-90-...item5af1b4d4ee

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